Aluminum, amine nitrate sensitized gel explosive compositions

A water gel explosive composition and process for preparing the same is provided which comprises an oxidizer, water, a gelling agent, and a crosslinker, and wherein the improvement comprises including therein from about 1 to about 10 weight percent of at least one amine nitrate sensitizer selected from the group comprising lower alkyl and alkanol amine nitrates and from about 1 to about 10 weight percent of an aluminum sensitizer having a surface area per unit weight of from about 3 to about 9 square meters per gram, said weight percentages based upon the total weight of the explosive composition.

BACKGROUND OF THE INVENTION 
This invention relates to water gel explosive compositions and particularly 
to incorporating therewith sensitizing amounts of certain amine nitrate 
sensitizers and an aluminum sensitizer having from about 3 to about 9 
square meters of surface area per gram. In another aspect, this invention 
relates to an improved water gel explosive composition wherein the 
sensitizing effects of paint grade aluminum are significantly enhanced by 
employing relatively small amounts of certain amine nitrate sensitizers. 
In a further aspect this invention relates to a process for producing 
water gel explosive compositions sensitized with a combination of paint 
grade aluminum and certain amine nitrate sensitizing agents. 
Modern water gel cap sensitive explosive compositions are, in some cases, 
sensitized by addition of some type of an alkyl or alkanol amine nitrate. 
Exemplary of an alkyl amine nitrate component is methylamine nitrate, 
which has, heretofore, been incorporated in relatively large weight 
percentage amounts in the water gel explosive composition in order to 
achieve sufficient sensitivity. Typically, at least between about 30 to 
about 40 weight percent of methylamine nitrate or similar amine nitrates 
has been required in order to produce a cap sensitive water gel explosive. 
Entrained air bubbles or microballoons must also be added to achieve the 
desired sensitivity. However, even with the use of such large quantities 
of methylamine nitrate, it has been found difficult to obtain low 
temperature detonatability below about 40.degree. to about 50.degree. F. 
Explosives having low temperature detonation characteristics are required 
for use in numerous applications, such as underground mines, and above 
ground applications, such as ditching operations in colder climates. 
Further, it is difficult to obtain water gel explosives which meet the air 
gap test standards (as further defined hereinafter) so as to be suitable 
for use as "permissibles" in mining operations even if relatively large 
amounts of amine nitrate sensitizers are employed. 
In order to provide a suitable amine nitrate component content in the 
explosive composition, highly concentrated water solutions of the amine 
nitrate component are required. Recent studies have shown that 
concentrated water solutions having greater than approximately 65 weight 
percent or more of the amine nitrate component are very sensitive to 
mechanical handling and are easily detonated by relatively low mechanical 
impulses. Thus, preparation of water gel cap sensitive explosive 
compositions, sensitized solely by large amounts of an amine nitrate 
component, can be extremely dangerous unless performed with care. An 
example of water gel explosives containing relatively large quantities of 
amine nitrates are the explosives described in U.S. Pat. No. 3,431,155, 
issued Mar. 4, 1969. 
Water gel cap sensitive explosive compositions have also been sensitized by 
other materials such as paint grade aluminum. These gels often contain 
from about 3 to about 6 weight percent paint grade aluminum. This 
sensitizer can be a very effective sensitizer, but it is difficult to 
handle because of severe dusting problems. Recently nondusting types of 
paint grade aluminum have been developed which partially alleviate these 
handling problems. However, there are limits on the maximum achievable 
sensitivity, and explosive compositions containing paint grade aluminum 
are not sufficiently sensitive for certain important applications. In this 
regard, it is difficult to achieve adequate cap sensitivity at 
temperatures at or below 40.degree. or 50.degree. F even when up to about 
7.5 percent paint grade aluminum is employed. Finally, paint grade 
aluminum sensitized water gel explosive compositions often have difficulty 
in detonating across a three inch air gap in the standard half cartridge 
test. This test is required by the Bureau of Mines for explosives which 
are to be employed in underground coal mining applications. Basically, the 
test requires that one half of a cartridge of explosive be able to 
detonate a second half across an air gap of at least 3 inches. Explosive 
compositions passing this test, and the other requirements of the Bureau 
of Mines, are referred to as "permissibles" in that use of the explosives 
is approved and permitted in underground coal mining procedures. The term 
"permissible explosives" as used herein is defined to mean explosive 
compositions which meet the standards set forth by the Bureau of Mines in 
30 C.F.R. 15, et seq. These standards include the above described air gap 
test as well as other requirements including, composition tolerances, 
propagation characteristics, gallery test requirements, poisonous gas 
production limits, and friction tolerances. Interestingly, the air gap 
sensitivity characteristics necessary to pass "permissible" standards and 
low temperature detonatability cannot be significantly improved by 
increasing the amount of paint grade aluminum in the water gel explosive 
compositions. 
In summary, although amine nitrate components as well as paint grade 
aluminum have been incorporated into water gel explosive compositions, 
these compositions have proved inadequate or marginal for certain, 
important field applications. Thus, U.S. Pat. No. 3,962,001 discloses 
explosive compositions having improved low temperature detonation 
characteristics which comprise hexamethylenetetramine and paint grade 
aluminum as well as nitric acid. However, such compositions must be 
prepared following critical process conditions which limit their 
commercial desirability. The present invention has been provided to remedy 
these deficiencies as the explosive compositions disclosed herein exhibit 
excellent low temperature detonability, and air gap sensitivity. 
SUMMARY OF THE INVENTION 
According to the present invention, a water gel explosive composition is 
provided which comprises an oxidizer, water, a gelling agent, and a 
crosslinker, and wherein the improvement comprises including from about 1 
to about 10 weight percent of at least one amine nitrate sensitizer 
selected from the group comprising lower alkyl and alkanol amine nitrates, 
and from about 1 to about 10 weight percent of an aluminum sensitizer, 
having a surface area per unit weight of from about 3 to about 9 square 
meters per gram, said weight percentages based upon the total weight of 
the explosive composition. It has been discovered that by employing 
relatively minor amounts of amine nitrate sensitizers in combination with 
such aluminum sensitizers a synergistic increase in low temperature 
detonability characteristics and in the sensitizing characteristics 
necessary to achieve the air gap detonation qualities required by the 
Bureau of Mines for "permissible" explosives, is achieved. 
DETAILED DESCRIPTION OF THE INVENTION 
According to the present invention, small sensitizing amounts of certain 
amine nitrates along with aluminum particles having relatively high 
surface area per unit weight interact as a dual sensitizer component which 
is incorporated in a water gel explosive composition to achieve low 
temperature detonation and sensitizing characteristics which were 
previously difficult to obtain in water gel explosive compositions. Water 
gel explosive compositions normally comprise at least an oxidizer, water, 
a gelling agent, and a cross-linking agent. The improvement disclosed 
herein comprises including in such a water gel explosive composition, from 
about 1 to about 10 weight percent of at least one amine nitrate 
sensitizer selected from the group comprising lower alkyl and alkanol 
amine nitrates and from about 1 to about 10 weight percent of an aluminum 
sensitizer having an average surface area of between about 3 to about 9 
sq. m/g, said weight percentages based upon the total weight of the 
explosive composition. The interaction of the two sensitizer components 
produces an explosive composition having detonation characteristics 
unexpectedly greater then when the aluminum or amine nitrates are used 
alone. 
The disclosed explosive compositions exhibit low temperature sensitivity 
which enable the explosive compositions to be detonatable at temperatures 
as low as 0.degree. F. An explosive composition having only paint grade 
aluminum as the sensitizer component and not incorporating any amine 
nitrates therein, is not cap sensitive below about 40.degree.-50.degree. 
F. Therefore, explosive compositions of the type disclosed herein, 
exhibiting low temperature detonatable characteristics, may be effectively 
used in numerous applications including use in underground mines where low 
temperatures are often encountered. 
The explosive compositions disclosed herein, having small amounts of 
certain amine nitrates in combination with paint grade aluminum or other 
aluminum sensitizing agents having comparable surface area per unit 
weight, also exhibit improved air gap sensitivity. Explosive compositions 
incorporating only paint grade aluminum are generally not detonatable 
across an air gap of more than 3 inches (as required by the Bureau of 
Mines standard half cartridge test for permissible explosives). The 
present explosive compositions increase the air gap sensitivity to a point 
where detonation occurs even across a 7 inch air gap. Thus, improved air 
gap sensitivity is achievable when the explosive compositions are prepared 
according to the process disclosed herein. 
Interestingly, the improved explosive compositions exhibit good low 
temperature detonability and air gap sensitivity characteristics even when 
sodium chloride is present. Sodium chloride is often incorporated in 
explosive compositions for the purpose of improving the incendivity 
characteristics of the explosive composition in natural gas-air and 
natural gas-air-coal dust mixtures. Thus, because of the extraordinary air 
gap sensitivity characteristics of the explosive compositions of the 
present invention (in some cases 7 inches or more) the addition of sodium 
chloride, while detrimental to air gap sensitivity does not reduce such 
sensitivity below the required 3 inch range. 
As discussed hereinbefore, it has been found that by incorporating small 
sensitizing amounts of certain amine nitrates with paint grade aluminum, 
an improved explosive composition is produced having unexpected 
characteristics. The amine nitrate sensitizers suitable for inclusion in 
the improved explosive composition herein are lower alkyl and alkanol 
amine nitrates. More than one of these amine nitrates may be included in 
the explosive composition, but generally only one amine nitrate sensitizer 
is utilized. The preferred amine nitrate sensitizer for incorporation in 
the improved explosive compositions is methylamine nitrate. However, other 
exemplary lower alkyl and alkanol amine nitrate sensitizers include 
ethylamine nitrate, ethanolamine nitrate, propanolamine nitrate, 
ethylenediamine dinitrate, and similar amine nitrates having from about 1 
to about 3 carbon atoms. 
Previously known explosive compositions have incorporated therein large 
amounts of similar amine nitrates to produce a water gel explosive 
composition. It has been found that the mere incorporation of small 
amounts of amine nitrate sensitizers, without paint grade aluminum, will 
not produce explosive compositions exhibiting the above-identified 
desirable characteristics. Moreover, the incorporation in explosive 
compositions of small amounts of amine nitrate with finely divided 
aluminum also does not produce a satisfactory explosive. However, it has 
been found that incorporation of small sensitizing amounts of at least one 
amine nitrate sensitizer discussed above with an aluminum sensitizing 
agent having an average surface area of from about 3 to about 9 sq. m/g, 
such as paint grade aluminum, will result in an explosive composition 
having characteristics superior to those previously known in the art. 
In this regard, the previous explosive compositions have incorporated 
usually from about 30 to about 40 weight percent of the amine nitrate 
sensitizer in the explosive composition. Applicant has found that the 
incorporation of only small sensitizing amounts of the amine nitrate, in 
combination with paint grade aluminum, produces an excellent explosive 
composition. Generally, the amine nitrate sensitizer should be included in 
amounts from about 1 to about 10 weight percentage, based upon the total 
weight of the explosive composition. In the preferred embodiment, the 
explosive composition should include from about 5 to about 10 weight 
percent of the amine nitrate sensitizer and most preferably about 8% 
thereof. 
Regarding the paint grade aluminum sensitizer, this constituent is utilized 
in the present explosive composition as a main sensitizer. This should be 
contrasted from those previously known explosive compositions which 
incorporate aluminum as an auxiliary fuel. The aluminum incorporated as an 
auxiliary fuel is generally divided or atomized aluminum which does not 
have the large surface area per unit weight characteristics of paint grade 
types of aluminum. It has been determined that if paint grade aluminum, or 
aluminum having relatively large surface areas per unit weight, is 
utilized in combination with the amine nitrate sensitizer, a superior 
explosive composition results. Generally, the aluminum sensitizer 
component should have a surface area per unit weight of between about 3 to 
about 9 sq. m/g, and, for economical reasons, preferably from about 5 to 
about 6 sq. m/g. Paint grade aluminum of both the dusting and nondusting 
varieties can be employed to achieve the improved characteristics of the 
compositions of the subject invention. This is contrasted with finely 
divided aluminum which is generally incorporated as an auxiliary fuel, and 
has surface areas of less than 1 sq. m/g, usually in the range of from 
about 0.05 to about 0.2 sq. m/g. Procedures useful in determining the 
surface area per unit weight of aluminum particles are set forth in Alcoa 
Aluminum Co.'s publication entitled "Quality Control and Analytical Test 
Methods for Alcoa Aluminum Powders", July 1975. 
In the preferred embodiment, a water gel explosive composition comprises 
from about 40 to about 80 weight percent oxidizer, from about 10 to about 
20 weight percent water, from about 0.1 to about 3 weight percent gelling 
agent, from about 0.02 to 0.3 weight percent cross-linking agent, from 
about 5 to about 10 weight percent of at least one amine nitrate 
sensitizer, and from about 3 to about 5 weight percent paint grade type 
aluminum sensitizer. Explosive compositions within those weight 
percentages exhibit the unique and unexpected characteristics of low 
temperature detonability, and increased air gap sensitivity. 
Fuels, such as particulate or finely divided aluminum, can be added to the 
composition for higher sensitivity or increased power output. Also, voids 
may be incorporated within the explosive composition mixture to increase 
the sensitivity thereof. For instance, air bubbles, hollow glass spheres, 
resin balloons, and perlite may be incorporated into the explosive 
composition. It is desired that the oxygen balance of the explosive 
compositions be between about -10 to about +10. To adjust the oxygen 
balance, liquid or solid fuels commonly used in the explosives art may be 
added to the present improved explosive composition. Examples include 
ethylene glycol, particulate aluminum and urea. 
Inorganic oxidizing agents which can be used to formulate explosive 
compositions of the subject invention include the nitrate and perchlorate 
salts of ammonium, alkali, or alkaline earth or Group III elements such as 
ammonium nitrate, sodium nitrate and sodium perchlorate, for example. 
Preferably, ammonium nitrate is employed as the main oxidizing agent in 
combination with one or more other suitable oxidizing agents, the ammonium 
nitrate comprising at least about 30% of the total explosive composition. 
For gelling the aqueous solution, the more conventional water soluble gums 
and gel modifiers, such as guar gum and chemically modified guars, can be 
used satisfactorily. Other examples of gelling agents and gel modifiers 
for the aqueous solution are carboxymethyl cellulose, methyl cellulose, 
synthetic polymers, polyacrylamides and polyvinyl alcohols. 
Suitable crosslinking agents for the gelling agents include polyvalent 
metal salts, borates, chromates, dichromates, antimonates, oxalates, and 
tartrates. Potassium pyroantimonate is an excellent cross-linker. 
When sodium chloride is employed to improve the incendivity properties of 
the composition, as much as 20% by weight of the composition can be used. 
However, large amounts of salt are detrimental to the detonation 
characteristics of the explosive composition and therefore sodium chloride 
is preferably employed in amounts range from about 3 to about 10% by 
weight of the composition.

EXAMPLES 
The following examples are presented to exemplify and illustrate the 
present invention to those of ordinary skill in the art and are not 
intended to limit the subject invention in any manner. 
EXAMPLE 1 
Water gel explosive compositions were prepared according to the subject 
invention in the following manner. First, approximately one-half of the 
water employed is heated to about 120.degree. F and all of the sodium 
nitrate, in prill form, and approximately one-half of the ammonium 
nitrate, in flake form, is dissolved therein. A water solution of the 
amine nitrate sensitizer is then admixed with the above solution, the 
amine nitrate having been dissolved in the remaining portion of the water 
which is to be added to the composition. Buffering agents such as ammonium 
phosphate are then added for pH adjustment. The remaining portion of 
ammonium nitrate, in prilled form, is then added to the aqueous solution. 
The aqueous gelling agent, premixed with a cross-linker therefor, is then 
added to the solution. High speed stirring or other means of agitation is 
then employed to incorporate air into the solution as it thickens. 
Finally, paint grade aluminum, mixed with ethylene glycol for ease in 
handling, is incorporated into the thickened solution. 
The above procedure was employed to produce water gel explosives having the 
compositions and densities set forth in Table I. 
TABLE I 
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1 2 3 4 
______________________________________ 
Ammonium Nitrate 43.3 55.6 63.7 43.2 
Sodium Nitrate 13.2 10.0 7.2 13.2 
Water 20.0 15.8 10.8 20.0 
Monomethylaminenitrate 
8.0 8.0 8.0 -- 
Monoethanolaminenitrate 
-- -- -- 8.0 
Sodium Chloride 5.0 -- -- 5.0 
Ammonium Phosphate 
-- 0.15 0.1 -- 
Guar Gum (and crosslinker) 
1.2 1.05 0.8 1.3 
Ethylene Glycol 5.3 5.4 5.4 5.3 
Paint Grade Aluminum 
4.0 4.0 4.0 4.0 
Density g/cc 1.16 1.15 1.17 1.15 
Low Temperature 
Detonability - #6 Cap 
10.degree. F 
0.degree. F 
10.degree. F 
30.degree. F 
Half Cartridge Air Gap 
5" 7" 6" 5" 
Test 
______________________________________ 
As can be seen from Table I these compositions exhibited excellent low 
temperature and gap detonation characteristics. 
EXAMPLE 2 
The following example is set forth to exemplify the synergistic effect on 
air gap sensitivity which has been discovered to be present when a 
combination of paint grade aluminum (or other particulate aluminum having 
relatively large surface areas per unit weight) is employed in combination 
with a relatively minor portion of an amine nitrate sensitizer. The 
compositions set forth below in Table II were prepared in substantially 
the same manner as was described in Example 1. 
TABLE II 
______________________________________ 
1 2 3 
______________________________________ 
Ammonium Nitrate 60.0 64.3 65.35 
Sodium Nitrate 5.0 5.6 10.0 
Water 16.0 20.0 18.0 
Monomethylaminenitrate 
8.0 -- 8.0 
Ammonium Phosphate 
0.2 0.1 0.1 
Ethyleneglycol -- 3.0 4.35 
Urea 6.0 -- -- 
Paint grade Aluminum 
4.0 6.0 3.25 
Guar Gum (and 0.8 1.0 0.95 
cross-linker) 
Density, g/cc 1.17 1.13 1.16 
Half Cartridge Air 
7" 2" 7" 
Gap Test 
Low Temperature 
Dependability &lt;14.degree. F 
40.degree. F 
.ltoreq.20.degree. F 
______________________________________ 
As can be seen from Table II the sensitivity of the compositions of columns 
1 and 3 to the half cartridge air gap test are greatly improved over the 
composition of column 2. Thus, the compositions of both columns 1 and 3 
would meet the air gap standards of the Bureau of Mines for "permissibles" 
for use in underground mining operations. The composition of column 2, 
which does not employ an amine nitrate sensitizer, would fail to meet 
those standards because of the air gap sensitivity of less than 3". 
While the invention has been described in relation to its preferred 
embodiments, it is to be understood that various modifications thereof 
will be apparent to those of ordinary skill in the art upon reading the 
specification, and it is intended to cover all such modifications which 
fall within the scope of the appended claims.