Note: Descriptions are shown in the official language in which they were submitted.
--1-- AET 37333
Low Density Explosives
Field of the Invention
The present invention relates to a low density
material, or structure, which can be used as an explosive
~er se, or can be used as an additive in conventional
explosive materials.
,,,,"
Description of the Related Art -
Semisolid colloidal dispersions of water-bearing
10 explosives (or blasting agents) are well known. These ;~
products typically comprise an oxidizing component, ~ ~ -
usually predominantly ammonium nitrate, a fuel component,
and water. These explosives are referred to in the art as
slurry explosives (or as water gels), and as
emulsion-type explosives.
Slurry explosives typically comprise a discontinuous ~
fuel phase which is dispersed in a continuous aqueous ~ `
solution of the oxidizer salt. Thickening agents are
added to the aqueous phase in order to increase the
vi~cosity of the explosive, or to effect gelation, and
thus stabilize the structure of the explosive.
Emulsion explosives typically comprise a
discontinuous aqueous oxidizer salt solution which is - ~ -~
dispersed in a continuous fuel phase. Emulsifying agents
;, ' I I i , ~ ' ! , , j ,
are generally added to the dispersion to stabilize the
dispersion.
The addition of additives to both slurry and emulsion
explosives to modify the performance of the explosive is
similarly well known. These additives include, for
example, the addition of TNT to the explosive to increase
the strength and/or sensitivity of the explosive.
Of particular interest in the present invention is
the addition of additives to create small voids within
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the explosive, which voids can be used to control the
density of the explosive, modify the detonation - -~
characteristics of the explosive, and/or increase the
sensitivity of the explosive. Typical sensitized `-
explosives were described, for example, by Cattermole et
al. in U.S. Patent No. 3,674,578.
One method of addition of void~ in an explosive, is
the addition of hollow glass microballons to an emulsion
explosive. While this method provides a suitable means
for the creation of voids within the explosive, the
microballons are relatively expensive and can be
difficult to handle due to their low bulk density.
Other products, similar to microballons, which
contain one or a number of gas bubbles are also used in
15 the explosives art. These other products include, for -
example, inorganic hollow micro-spheres made of glass,
slrasu (Japanese volcanic ash), silicon sand, or sodium
silicate and the like. These materials generally suffer
from the same disadvantages as glass microballons.
Edamura et al. disclose, in U.S. Patent No.
4,543,137, the use of a gas-retaining agent such as those
made from foamed polystyrene, foamed polyurethane and the
like. The gas-retaining agents of Edamura et al. can have
a rigid structure, similar to the inorganic microballons
doscribed hereinabove, and can be brittle and sub~ect to
breakage during handling, or can be made soft and spongy
so as to be more resistant to inadvertent breakage during
handling.
These soft and spongy gas-retaining agents are
produced by foaming a foaming agent in a thermoplastic
resin and allowing the thermoplastic resin to set and
thus entrap gas within the resin structure.
However, this route of adding gas voids to the
explosive requires the use of a thermoplastic resin which
will only act as a fuel when the explosive is detonated.
In-situ generation of air or gas voids within the ;
explosive is an alternative method over the addition of
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gas filled microballons, and typically comprises the -
addition of a material which reacts in the explosive to
generate a gas bubble. This gas bubble is entrained
within the explosive by the viscous nature of the
semisolid explosive. The generation of a gas void within
the explosive by an in-situ chemical reaction is termed ;~
within the industry as chemical gassing, and is described
in numerous patents, such as U.S. Patent Nos. 3,886,010 ~ -
and 3,706,607. In these patents, the use of chemical ;~
gassing agents such as nitrites, weak acids, hydrazine
and peroxides in slurry and/or emulsion explosives is
described.
While chemical gassing is practiced in the industry, ~ --
its use is limited because of the dlfficulty in
controlling the reaction rate of the chemical gassing
reaction. The degree of gassing may be insufficient, or
may be excessively slow, under cold production
temperatures.
A third route to introducing gas voids into an
explosive is to mechanically agitate the explosive
composition in order to entrain an occluded gas void
within the explosive. This route has the disadvantage of ~
intensive mechanical agitation of a sensitized explosive, ~-
and can be subject to poor long-term blasting stability
as gas is slowly lost from the explosive.
A further route to the production of gas voids within
an explosive explosive is described by Curtin and Yates
in U.K.~ Patent Applic,atjiqn No. 2,179,035, wherein a gas
bubble generating agent is added to the explosive prior
to, or while, the explosive is subjected to
super-atmospheric pressure to dissolve at least part of
the gas present. The explosive is returned rapidly to
atmospheric pressure and thus creates a fine
discontinuous gaseous phase in the composition. However,
35 this production route requires the sensitized explosive ~`
to be prepared under pressure, and thus requires
specialized equipment adapted to handle the pressurized `~
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explosive.
In our copending Canadian patent application No.
2,040,346, laid-open on October 13, 1992, an explosive
composition is described wherein the explosive is
5 sensitized by the addition of a gas-in-liquid foam which -
has been stabilized by the addition of a foaming agent to
the foam. In our further copending~U.S. patent --;
application No. 07/866,023 filed April 9, 1992, a foam
composition is described which can be prepared from a
lo variety of materials, however, the foam is used as a ;
gas-in-liquid material. ~ -~
In light of the problems presented hereinabove, it is
an ob~ect of the present invention to provide a low
density material which acts as an explosive, and which
15 may be included in an emulsion, slurry, dry blasting ~ -
agent, or dynamite, to lower the density of the explosive
or modify its performance.
Summary of the Invention
Accordingly, the present invention provides a
structure comprised of a gas-in-solid foam characterized
by a density of less than about 1.0 g/ml wherein said ~;
structure is comprised of an admixture of a single or
plurality of foaming agents, and/or a carrier, together
with a single or plurality of inorganic or organic
materials, and combinations thereof and therebetween,
which structure is liquid at foaming temperatures, and
wherein said structure is characterized by being below ~ ;
the solid/liquid phase transition point of said materials ; ;
so that said materials are solid.
Various materials may be utilized in the practise of
the present invention. Preferred materials include those
which are solid at ambient temperatures of about 20-C but
which will form a liguefied melt or a solution,
preferably a saturated aqueous solution, at elevated
temperatures. It is preferred that these elevated
- - 2 l l 3 ~
temperatures fall within the range of 50OC to lOO C. ; -
These materials can include urea, or salts such as sodium
chloride, or sodium nitrate. Further preferred materials
are various organic compounds which meet the criteria set ~ -
out hereinabove. These materials may include compounds
normally used as explosives on their own, such as
trinitrotoluene (TNT), which co~pounds allow the blast
properties of the explosives prepared in accordance with -
the present invention to be modified, in addition having
thair density lowered.
Preferred salts include salts which are traditionally
known in the explosives industry as oxidizer salts. These
salts include, for example, nitrates, chlorates, and
perchlorates. Particularly preferred salts are alkali or
alkali earth metal nitrate salts, which salts include,
for example, sodium nitrate, potassium nitrate, and the
like, or mixtures thereof. Most preferably, however, the
salt is ammonium nitrate.
A preferred carrier is water, so as to form agueous ~-
solutions of the inorganic and/or organic materials,
where appropriate. However, the carrier may be any liquid
substance, or substance which is compatible with the
structure being prepared which is liquefiable at the foam
Porming temperature.
The term "foam" in this document is used to describe
a mass of gas bubbles which have been dispersed in a
semi-saturated or saturated liquefied material or
solution. The term "gas-in-solid foam" describes a foamed
material wherein the material has solidified to a solid
30 structure when the material is cooled to a temperature ~ ~ `
below the solid/liquid phase transition point. This
"gas-in-solid" foam is distinguished from a
"gas-in-liquid" foam wherein the foam wall structure is
maintained as a flexible liquid film.
Most of the volume of a foam is the gas phase, and
typically, the gas phase may comprise at least 90% by
volume for the lesser density foams. The bubbles formed ~ ~
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in the foam are essentially all closed cells, ie the gas ;
bubbles are surrounded by, and thus separated from each
other, by thin, flexible films of the liquefied salt or
compound melt or solution. However, as the foam cools, -
5 the salt or compound solidifies as the temperature -
decreases below the solid/liquid phase transition point
of the salt or compound. The solidified salt or compound
thus forms, within the flexible film, a rigid film around
the gas bubbles. This rigid film has a number of cells
which cells may be open or closed or some combination
thereof.
Where the salt or compound forms crystals upon being
cooled below the solid/liquid phase transition point, the
solidification of the solid may be termed
"crystallization". However, use of this term merely
implies that the salt or compound has solidified at a
temperature of less than the solid/liquid phase
transition point.
In the case of ammonium nitrate, as an example of the
20 present invention, the cooled foam made from a saturated -
aqueous solution, is a soft sponge-like material having
crysta~s of ammonium nitrate present in the film ~ -
surrounding the gas bubble. This ~gas-in-solid foam" ; -
~ormed may be blended into an emulsion explosive, or the ~
25 like, to reduce the density of the emulsion. - -
The foam may also be dried or freeze-dried to remove
any remaining carrier liquid, such as water. This "dried"
~or more generally, solvent-free) material changes from
the sponge-like material to become hard and brittle, and
may be crushed and broken up into smaller fragments with
open and closed cell structure, which can be added to,
for example, a compatible explosive in a manner similar
to the addition o~ glass microballons in the prior art. ~ -
When broken, the powdered material has a collection of ` -
35 open and closed cells, and still provides a density ~-
lowering effect when blended into an e~ulsion explosive.
Alternatively, the dried material may exhibit
2 ~ 1 3 ~
explosive properties of its own, and may be used as a low
density explosive.
The gas-in-solid foams of the present invention may
be produced by mechanical agitation of the liquefied
material ko entrain the gas voids within the liquid
carrier. This operation is preferably conducted at
temperatures just abo~e the solid/liquid phase transition
point, or crystallization temperature, of the material in
order that the foam can be cooled to effect
lo solidification and/or crystallization, and thus
effectively ~lock-in~ the foamed structure. A preferred
temperature range for forming the foam is about 5 to lO-C
above the solid/liquid phase transition, or
crystallization, te~perature.
Maintaining the foam at temperatures above the
solid/liquid phase transition point, or crystallization
point, of the salt or co~pound allows the liquid material
to drain from the foam, and thus reduce the size of the
film layer between gas bubbles. This is of use in the
production of ultra-low density foams, but has the risk
that the foam structure may disintegrate before ~--
solidlfication, or crystallization, of the material,
occurs.
In order to effectively lower the density of the
25 explosive, the gas-in-solid foams of the present ;~
invention preferably have a low density. In its role as a ~-
density reducing agent, the gas-in-solid foam preferably -
has a dansity of less, than 1.0 g~ml, more preferably
below 0.5 g/ml and even more preferably below 0.2 g/ml. ~; ;
~he foams may also be produced by introducing or
"sparging" a pressurized gas into a pressurized liquid
component of the foam, and subsequently releasing the
pressure on the system so as to create small gas bubbles
within the liquid component. Again, the foam is cooled to
effect crystallization, or solidification, and form the
gas-in-solid foam.
Preferably, however, the foams of the present
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invention are prepared by a process for producing a
gas-in-solid foam structure comprising heating a mixture
of a foaming agent and/or a carrier, together with a
single or plurality of inorganic or organic materials,
and combinations thereof and therebetween, to a
temperature above the solid/liquid phase transition point
of said material, agitating said mixture to entrain gas
bubbles within said mixture to form a gas-in-liquid foam;
and cooling said mixture to a temperature below said
solid/liquid phase transition point to form a
gas-in-solid foam. ~-
The gas-in-solid foam structures of the present
invention may be an explosive ~er se, or may be an
non-explosive additive which may be added to various
explosives in order to produce low density explosives.
Accordingly, the present invention also provides a low
density explosive comprising: ~ `
i) an oil-based fuel phase, ;
ii) an oxidizer salt phase, and
iii) a structure as described hereinabove.
Preferably, the explosive is an emulsion explosive
comprising: ~
i) a base emulsion explosive comprising a continuous ;- ;
oil phase, a discontinuous aqueous oxidizer salt phase,
25 and an emulsifier: and -
ii) a gas-in-solid foam structure as described `~
hereinabove.
The foams of the present invention are preferablyj ;
added to the explosive composition by a low shear mixing
technique such as a static mixer, or a ribbon mixer.
During addition of the foam, the foam, either as a
liqu~d-containinq sponge-like material or as a dried
powder, is merely dispersed within the explosive
composition. At this stage, there is generally no need
for intense mechanical agitation to entrain additional
gas voids within the explosive composition.
The presence of a gas bubble stabilizer in the ~
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emulsion may be beneficial during addition of the
sponge-like material in order to aid gas retention.
The gas used to form the bubbles in the foams of the
present invention may be any gas which is compatible with
other components of the explosive. Preferably, the gas is
air, carbon dioxide, or nitrogen, but any other gas could
be used provided that the solubility of the gas in the
liquid is controllable over the time and temperature
range to which the sensitized explosive will be stored
prior to use.
Control of the drainage rate before solidification,
and thus control of the half-life of the gas-in-precursor
liquid foam can be influenced, and effectively
controlled, by the selection of the foaming agent. Any
15 suitable foaming agent may be added to the foam in order ~ ;~
to stabilize the liquid film around the bubble. ;~
The foaming agent stabilizes the film around the gas -~
bubbles in order to prevent them from bursting or ;
coalescing prior to solidification of the salt or
compound as the material is cooled below the solid/liquid
phase transition point. Typical foaming agents would
include materials such as milk, egg, animal, vegetable,
or fish proteins, such as for example, egg albumin or
casein, or polysaccharides or starches, such as dextrin,
25 agar and guar, or the like, and any mixture thereof. The ;
foaming agent can also be a protein derivative or
associated product such as phospholipids, lipoproteins,
collagens, hyqrolyseq proteins,and globulins. Steroids
may also be used as a foaming agent.
The foaming agent may also include water soluble or
di8persible surfactants such as, for example, FC , FC-92 , ;
FC-100 , FC751 , which are all perfluorinated surfactants,
or mixtures with other water soluble or water dispersible
surfactants. Other foaming agents include, for example,
derivatives of succinic anhydride, steryl octazylene
phosphate and certain fatty alcohols. ;
As described hereinabove, the carrier used to prepare
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2 l 13~3
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the foam is a material which is a liquid or a material
which is a liquid at-foam forming temperatures. The
carrier is also preferably compatible with the continuous
phase of the explosive. The additives of the foaming
solution can be dispersed or dissolved into the carrier.
The carrier may, however, take part in the detonation as
a fuel, an oxidizer, a sensitizer,~or it may be inert.
The foam can be added to sensitize any suitable
explosive material wherein gas voids are advantageous.
Explosive materials include, in particular, emulsion or
slurry explosives, ANFO, low density ANFO, Heavy ANFO,
and the like, but also includes propellants, high heave
explosives, modified emulsions, cast explosives, nitro ;
ester based systems, and TNT, RDX or NG based systems. -
These explosive compositions are generally well known to
the skilled artisan, and are generally well described in ; ~-
the prior art. -
The explosive compositions of the present invention
may also comprise additional additives to enhance or
modify the properties of the explosive. The use of these
additives is commonly known within the explosives
industry, and include the solid dopes and sensitizers -
commonly added to emulsions such as aluminum, ~`~
ferrosilicon, TNT (trinitrotoluene), AN (ammonium ;;~ ~
25 nitrate), MAN (methylaminenitrate), PETN (pentaerythritol ~;
tetranitrate) and the like. Further, additional
sensitizing agents, such as for example, glass
microballons, may also be used in combination with the
,
foams of the present invention. ;~
Examples
The invention will now be described, by way of ;~
example only, by reference to the following examples. '
Ex--amDle 1
Various foams were prepared in order to demonstrate ~-
2i139~
the ability to form a low density material. The foams
were all prepared by the following procedure. An aqueous
solution of a salt such as ammonium nitrate, sodium -
nitrate, or sodium chloride, or a liquefied melt
comprising, for example, ammonium nitrate and/or sodium
nitrate, or urea, was heated in order to liquefy the
material. A foaming agent, or mixture of foaming agents
was added to the heated aqueous sol~tion, and the ~ ~-
resultant mixture was rapidly agitated to produce a foam.
The foamed material was then cooled to allow the salt or
compound to solidify as the temperature decreased below ` -
the solid/liquid transition point, and thus lock-in the
structure of the foam. The resultant foam was oven dried
if water was present, and the final foam density was
measured. The results of Example 1 are set out in Table
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Table 1: Foamed Material Exam~les
Mixing
Run No. Solution Temp. Foaming Dry Foam
(-C) System Density :-
q~ml :
1 81% AN 55 2% Albumin
19% Water 0.66%Guar T4072 0.283
97.34% Solution . ~
2 81% AN 55 2% Albumin 0.136 ~ -
19% Water 98% Solution
3 81% AN 90 2% Albumin
19% Water 2% Dextrin No Foam .
96% Solution
4 81% AN 55 2% Albumin : ~:
19% Water 2% Dextrin 0.222 :~
96% Solution
75% AN 50 2% Albumin
25% Water 2% Sodium Alginate 0.245 .
96% Solution . .
20 6 81% AN 55 2% Albumin .. -
19% Water 2% Agar 0.193
96% Solution ~ ~ :
7 81% AN 55 2% Albumin Poor .
19% Water 2% Acrylamide Foam `
96% Solution ~:
8 81% AN 55 3% FC 0.026
19% Water 97% Solution ~ .
9 81% AN 55 3% FC 100
. 19% Water 3% Methyl Cellulose 0.034 . :~
94% Solution i ;
81% AN ' '55 3% FC 100 ~ : ;.:;
19% Water L0% Dextrin 0.326
87% Solution
11 80% AN 55 3% FC 100
20% Water 10% Silica gel 0.0349 : :-
87% Solution
12 80% AN 55 10% Texapon EX40 0.813
20% Water 90% Solution
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13 80% AN 55 15% Texapon EX40 0.475
20% Water 85% Solution ~ ~:
14 80% AN 55 22% Texapon EX40 0.182 -:~
20% Water 78% Solution
,
lS 64% AN 70 3% FC 100 ~ "~
13% SN 97% Solution 0.06 -~
23% Urea ~:~
16 50% AN 30 3% Caf~ein
50% Water 2% Sodium Dodecyl 0.03
Sulphate
95% Solution :~
17 55~ AN 30 O.S% Dodecyl Phenol :~
45% Water 1% Collagen -`~
1.5% Casein OfO5 . :
4% FC 100
93% Solution
18 55% AN 30 3% FC 751 ~::
45% Water 3% Casein 0.05
94% Solution
19 25% NaCl 75 2.7% Albumin
75% Water 8.8% Dextrin 0.166 ::
88.5% Solution
58.3% SN 71 2.7% Albumin
41.7% Water 8.8% Dextrin 0.148 . :~-
88.5% Solution
Notes~
AN - Ammonium nitrate SN = Sodium nitrate
FC, FC 100, FC751 = Perfluorinated surfactants
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The gas-in-solid foams produced in Example 1
demonstrate that low density dried foams can be prepared
from a variety of materials. The density of the foam is
dependent upon, inter alia, the solution inqredients, the ~-
5 foaming system selected, the temperature, and the -
agitation time and effectiveness. A stable foam could not
be prepared with Run No. 3 due to the high temperature
used. However, a gas-in-solid foams was prepared using
the exact same foaming system at a temperature of 55-C
(Run No. 4).
Exam~le 2 ~ `
A series of emulsion explosives were prepared which
incorporated various gas-in-solid foam low density ~; `
materials as described in Example 1. The base emulsion
explosive was prepared in accordance with known
techniques by mixing a heated (90-C) aqueous solution of
an oxidizer salt, such as ammonium nitrate and/or sodium ~
nitrate, with a heated oil fuel phase, optionally in the ` `
presence of an emulsifying agent. The base emulsion was
cooled, and the low density explosive additive, was
added. The resultant sensitized emulsion explosive was
cooled to ambient temperature, and its detonation
properties were measured.
:: -~
Run No . 22 ~ ;~
Base Emulsion: 93.9% AN/SN/Water
(77% AN/11% SN/12% Water)
6.9% Oil Ph~ase
0.1% FC-740
Foam Additive: From Example 1, Run No. 4
Emulsion Explosive: 3.0 Kg of base emulsion was
cooled to 75-C and blended with
452 g of Foam Additive. The ;
resultant explosive had a
density of 1.16 g/ml.
Detonation Results: In a 2.5 inch (6.2 cm~ diameter
cartridge, using a 20 g
Pentolite primer, the velocity -
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-15-
of detonation ~VOD) was measured
at 3.92 Km/sec.
Run No. 23
~ . . . ~, .
Base Emulsion: 93% AN/Water (81% AN/19% Water) ;~
7% Oil Phase - ~
Foam Additive: From Example 1, Run No. 4 ~ ~ ;
Emulsion Explosive: Prepared aS described in Run No. ;
22. The resultant explosive had
a density of l.lS g~ml. ;;~
Detonation Results: In a 3 inch (7.6 cm) diameter
cartridge, using a 20 g
Pentolite primer, the VOD was
measured at 4.7 Km/sec. ~ ~-
-:
lS Example 2 clearly demonstrates that sensitized
emulsion explosives can be prepared using the
gas-in-solid foam additive of the present invention.
:; ~
Example 3
Since the gas-in-solid foamed nitrate additives
contain a mixture of nitrate and organic material, they
can act as explosives ~er se. Accordingly, a foamed AN
material was used to produce a variety of different
explosives.
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Run No~ 24 ~ `
~ .
1 Xg of the starting composition of Example 1, Run
No. 4, was blended with 1 Kg of Ampal 60i atomized
aluminum, and the resultant mixture was foamed. The ~-~
mixture was dried and had a final density of 0.136 g/ml. ;~
The mixture was packaged in a 1 inch (2.5 cm) diameter
cartridge. When initiated with an EB cap, the mixture had
a VOD of 1.83 Km/sec.
. ~ -. ~ . . : .
2 ~ 4 ~
--16--
~un No . 2 5
~: .
1 Kg of the foamed AN from Example 1, Run No. 4, was
blended with 65 g of Fuel Oil. The mixture was pacXaged
in 2 inch (5 cm) diameter cartridges. When initiated with
an EB cap, the mixture had a VOD of 2.0 Km/sec.
Run No. 26
1 Kg of the foamed AN from Example 1, Run No. 4, was
blended with 1 Kg of AN prills. The mixture was packaged
in a 1 inch (2.s cm) diameter cartridge. When initiated ;
10 with an EB cap, the mixture had a VOD of 1.8 Km/sec. - ~
~ .. ,i. .., ~,
Exam~le 4
A series of emulsion explosives were prepared using ~ i
the foamed sodium chloride material produced in Example
1, Run No. 19. The foamed material was added to an
unsensitized commercial emulsion explosive, having an
unsensitized density of 1.45 g/ml, in the ratio of 3000
grams of emulsion to 450 grams of foam. The explosives
prepared were packaged in a variety of cartridge sizes,
and the ability of the material to detonate was measure.
: . ,
Run No. 27
The mixture was packaged in a 3 inch (7.5 cm)
diameter cartridge, and had a cartridged density of 1.25
g/ml. When initiated with a 40 gram primer, the sample
detonated.
Run No. 28
The mixture was packaged in a 3 inch (7.5 cm)
diameter cartridge, and had a cartridged density of 1.24
g/ml. When initiated with a 3 gram primer, the sample
detonated.
F~
:- 2~3945
-17- -
Run No. 29
The mixture was packaged in a 2 inch (5 cm) diameter
cartridge, and had a cartridged density of 1.16 g/ml.
When initiated with an 80 gram primer, the sample
detonated.
Run No. 30
The mixture was packaged in a 2 inch (5 cm) diameter
cartridge, and had a density of 1.16 g/ml. When initiated
with a 12 gram primer, the sample detonated.
Having described specific embodiments of the present
invention, it will be understood that modifications -~
thereof may be suggested to those skilled in the art, and
it is intended to cover all such modifications as fall ;~
within the scope of the appended claims. ~, ;
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