Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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CAST EXPLOSIVE COMPOSITION AND METHOD
The present invention relates to a cast explosive
composition and other energetic compositions such as
propellants. (As used herein, the term "explosive" also shall
include other energetic compositions such as propellants.)
More particularly, the invention relates to a cast explosive
composition which is initially formed as a stable, fluid,
water-containing, water-in-oil emulsion explosive and which
thereafter solidifies upon the addition of a desiccant and/or
emulsion destabilizing agent. As used herein, the term
"desiccant" means a water reacting, absorbing or adsorbing
agent. One method of the present invention is the formulating
of the cast explosive composition by adding the desiccant
and/or destabilizing agent to a stable emulsion to cause the
emulsion to solidify. Alternatively, a desiccant can be
included in the aqueous phase of the stable emulsion which
then is solidified by the addition of an emulsion destabilizing
agent. A further method relates to the loading of a container
with the cast explosive composition. As used herein, the
terms "cast" and "solidify" refer to an unflowable or
relatively unextrudable mass of finely knitted oxidizer salt
crystals which have crystallized from an aqueous solution.
Water-in-oil emulsion explosives are well known in the
art. See, for example, U.S. Patent Nos. 4,356,044; 4,322,258;
and 4,141,767. Such explosives contain a continuous phase of
a water-immiscible organic liquid fuel and a discontinuous
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phase of an emulsified inorganic oxidizer salt solution.
Normally, these explosive compositions contain a density
reducing agent for sensitivity purposes. These compositions
have a grease-like consistency which renders them water-
resistant and generally easily extrudable.
More recently, cast explosive compositions formed from an
unstable water-in-oil emulsion have been disclosed. In U.S.
Patent Nos. 4,548,659 and 4,566,919, cast explosive
compositions are formulated at an elevated temperature by
forming a water-in-oil emulsion, which, when allowed to cool,
forms a cast composition due to the weakening or breakdown of
the inherently unstable emulsion phase and subsequent
crystallization of the oxidizer salt. European Patent
Application No. 0152060 suggests that cast compositions can be
formed from a stable water-in-oil emulsion by adding a
surfactant to cause the breakdown of the emulsion and
crystallization of the inorganic oxidizer salt in solution.
This patent application, however, pertains to anhydrous water-
in-oil emulsions, which are inherently less stable than those
containing water.
SUMMARY OF THE INVENTION
The present invention provides a means whereby a cast
explosive composition can be formed from a stable water-in-oil
emulsion explosive that contains a significant amount of
water. This can be accomplished in several ways. A desiccant
can be included in the continuous aqueous phase of the stable
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emulsion, and an emulsion destabilizing agent can be added in
an ~mount sufficient to cause the explosive to solidify.
Alternatively, the desiccant and/or emulsion destabilizing
agent can be separately or jointly added to the stable
emulsion. By "added" is meant to mix the additive throughout
the emulsion sufficient to cause the emulsion to breakdown and
solidify.
A particular advantage of forming a cast explosive
composition according to the present invention is that a
stable emulsion explosive can be formulated at an elevated
temperature, cooled, and stored or transported as desired,
prior to adding the desiccant or emulsion destabilizing agent
or both to cause the explosive to solidify. Thus handling of
the emulsion at an elevated temperature is minimized. In
addition, temperature-sensitive ingredients such as metallic
particles or compound explosives can be added to the stable
emulsion after it has cooled to ambient temperature but prior
to, or at the same time as, the addition of the desiccant
and/or destabilizing agent. In this way highly sensitive
ingredients can be incorporated into a cast explosive
composition at relatively safe temperatures.
DETAILED DESCRIPTION OF THE INVENTION
Prior to the addition of the desiccant and/or
destabilizing agent and subsequent solidification, the
compositions of the present invention haveagrease-like
consistency and are in the form of a water-in-oil emulsion.
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This is advantageous for a number of reasons. The emulsion
form allows droplets of aqueous oxidizer salt solution to be
finely and intimately dispersed throughout the continuous fuel
phase. As the stable emulsion cools from its elevated
formulation temperature, precipitation of the salts within the
small droplets is physically inhibited. Thus the intimate
dispersion is maintained which results in increased reactivity
between oxidizer and fuel. Even upon the destabilization of
the emulsion and subsequent crystallization of the salts, the
intimacy of oxidizer and fuel dispersion is largely
maintained. Another advantage is that prior to
destabilization, the grease-like emulsion is fluid and can be
pumped, extruded or further mixed as desired. Thus
temperature-sensitive ingredients, such as compound explosives,
can be added to and mixed throughout the composition at a
temperature (normally ambient) below the elevated formulation
temperature of the emulsion, and thus at a temperature at
which the sensitive ingredients can be added safeIy. Further
advantages are that by cooling the emulsion prior to casting,
shrinkage and/or cavity formation after placement into a
container can be minimized and containers need not be cooled
as in typical melt cast operations. Still further, the risks
to personnel associated with the handling of high temperature
material can be reduced.
A preferred ingredient of the present invention is a
desiccant, which will react with, absorb or adsorb the water
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in the aqueous phase of the emulsion, upon destabilization of
the emulsion. This interaction thereby contributes to the
desired cast characteristics of the final product. Preferably,
sufficient desiccant is included to hydrate substantially
all of the water in the composition.
The desiccant preferably is present in an amount of from
about 0.5% by weight of the total composition to about 15% and
can be selected from (1) nitrate, perchlorate, chlorate,
sulfate, hydrogen sulfate and chloride salts of various metals
including but not limited to magnesium, calcium, aluminum,
sodium, lithium, zinc, iron and copper, (2) various other
anion/cation salts such as phosphates, carbonates and
acetates, (3) various dessicants that depend on physical
absorption such as silica, alumina and charcoal, or (4)
metallic oxides, such as magnesium and calcium oxide, which
can act directly as desiccants or can be reacted in situ,
i.e., with acids, water or by metathesis, to form desiccating
salts, and (5) materials which react with water such as acid
anhydrides, acid halides, isocyanates and esters.
The inorganic oxidizer salt is employed in an amount of
from about 35% to about 95% by weight of the total
composition. The oxidizer salt(s) can be selected from
ammonium, alkali and alkaline earth metal nitrates, chlorates
and perchlorates or mixtures thereof. The oxidizer salt
preferably is primarily ammonium nitrate (AN) but other salts
may be employed as well. If AN is used as the primary salt,
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then other salts preferably are used in an amount of up to
about 20~. From about 10% to about 65% of the total oxidizer
salt may be added in particle or prill form.
The immiscible organic liquid fuel forming the continuous
phase of the composition at the time of its formulation at an
elevated temperature, and prior to solidification, is present
generally in an amount of from about 2% to about lS% or more
by weight of the total composition. The actual amount used
can be varied depending upon the particular immiscible fuel(s)
used and upon the presence of other fuels, if any, and upon
the intended application of the product. The immiscible
organic liquid fuels can be aliphatic, alicylic and/or
aromatic, can be saturated and/or unsaturated, and can be
polymeric or polymerizable, so long as they are liquid at the
formulation temperature. Preferred fuels include mineral oil,
waxes, paraffin oils, benzene, toluene, xylenes and mixtures
of liquid hydrocarbons generally referred to as petroleum
distillates such as gasoline, kerosene and diesel fuel.
Particularly preferred liquid fuels are mineral oil, No. 2
fuel oil, paraffin waxes, microcrystalline waxes and mixtures
thereof. Aliphatic and aromatic nitro-compounds also can be
used. Halogenated organic materials can be used in amounts up
to about 25%. Mixtures of the above can be used.
Water is employed as an essential ingredient and
functions as a solvent in the oxidizer salt solution in an
amount of from at least about 1~ to about 10% by weight of the
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emulsion phase, and preferably in an amount of from about 3%
to about 10%, since the emulsion tends to be more stable at
higher water contents. Water miscible organic liquids can
partially replace water as a solvent for the salts, and such
liquids also function as a fuel for the composition. Miscible
liquid fuels can include alcohols such as methyl alcohol,
~lycols such as ethylene glycol, amides such as formamide, and
analogous nitrogen-containing liquids. The use of water
allows for a lower formulation temperature since it lowers the
crystallization temperature of the oxidizer salt solution.
Water also increases the stability of the emulsion until such
time as the emulsion intentionally is destabilized and the
composition solidified. It is because of the presence of water
that the desiccant preferably is employed to bind the water and
enhance the solid characteristics of the final composition.
Optionally, and in addition to the immiscible liquid
organic fuel, solid or other liquid fuels or both can be
employed in selected amounts. Examples of solid fuels which
can be used are finely divided aluminum particles; finely
divided carbonaceous materials such as gilsonite or coal;
finely divided vegetable grain such as wheat; and sulfur.
Liquid fuels include those water-immiscible fuels described
above. A particularly preferred solid fuel is particulate
aluminum which can be employed in amounts up to about 50% by
weight to increase the density and energy of the composition.
Although granular, atomized or paint grade aluminum can be
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used, atomized is preferred.
Sensitizers can be employed to increase the compositions'
sensitivity to detonation. They can be liquid or solid and
can comprise compound explosives, particulate metals such as
aluminum and mixtures of these ingredients. Particulate
aluminum can be used in amounts up to about 50% by weight, and
compound or molecular explosives may be used in an amount up
to about 70% by weight. Examples of particulate compound
explosives are pentaerythritol tetranitrate (PETN),
cyclotrimethylene trinitramine (RDX), trinitrotoluene (TNT),
cyclotetramethylene tetranitramine (HMX), and nitrocellulose.
Other types of compound explosives are water soluble salts
such as amine nitrates or perchlorates, including monomethylamine
or ethylenediamine nitrates, and alkanolamine salts such as
ethanolamine nitrate or perchlorate. A preferred sensitizer is
RDX, alone or in combination with atomized aluminum.
The emulsion destabilizing agent is any agent that will
cause destabilization of the emulsion so that solidification
can occur and generally is employed in an amount of from a
trace to about 15% by weight of the total composition.
Emulsion solidification can be caused by disruption of the
emulsion structure either chemically or physically. Chemical
disruption of the emulsion by surface active liquids or solids
or by various solvents is thought to cause alterations in the
interfacial structure of the emulsion, thus allowing oxidizer
droplets to coalesce and subsequent crystallization to
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occur. Another possible form of chemical disruption is that
some surface active agents may cause a gradual inversion of
the water-in-oil emulsion to an oil-in-water emulsion, thus
allowing crystallization to occur. Physical disruption of the
emulsion structure by particulate matter, which can serve as
nucleation sites for crystal growth, is another possible
mechanism. Such particulates may also be surface active so
that a combination of mechanisms may be involved. Examples of
the emulsion destabilizaing agent are (1) various ionic
surfactants, typically oil-in-water surfactants, including:
ethoxylated or nonethoxylated alkyl, aryl or alkyl aryl
sulfonates, such as sodium alkyl naphthalene sulfonate;
phosphates; carboxylates and amines; t2) various alkyl, aryl
or alkyl aryl nonionic or ethoxylated nonionic surfactants
such as ethoxylated alkyl phenols; (3) various surface active
solids such as clays, aluminas and silicas and (4) various
solvents such as alcohols, ethers, esters, ketones and organic
acids. Such agent(s) can be added in any amount necessary to
cause destabilization, but generally this amount is less than
10% by weight.
The emulsifier of the present invention can be sPlected
from those conventionally employed, and various types are
listed in the above-referenced patents. The emulsifier is
employed in an amount of from about 0.2% to about 5% by
weight. It preferably is employed in an amount of from about
1% to about 3%. Typical emulsifiers include sorbitan fatty
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acid esters, glycol esters, substituted oxazolines, alkyl
amines or their salts, derivatives thereof and the like.
Preferably the emulsifier contains an unsaturated hydrocarbon
chain as its lipophilic portion, although the saturated form
also can be used.
Although it is desirable that the compositions of the
present invention have a high density, the compositions can be
reduced from their natural densities by addition of a density
reducing agent, such as small hollow particles of which
plastic or glass spheres and perlite are examples. In
addition, gas bubbles can be entrained into the composition
during formulation or can be introduced by a small amount of a
chemical gassing agent, such as sodium nitrite, which reacts
chemically in the composition to produce gas bubbles. The use
of density reducing agents to increase sensitivity is well
known in the art.
The compositions of the present invention are formulated
by first forming an aqueous solution of the oxidizer salt(s)
at an elevated temperature above the salt crystallization or
solidification temperature. Optionally a desiccant can be
included in the aqueous soiution. This solution then is
combined with a solution of the emulsifier and the immiscible
organic liquid fuel, which can be at ambient or an elevated
temperature, and mixed with sufficient visor to produce an
emulsion of the oxidizer salt solution in a continuous organic
liquid fuel phase. Usually this can be accomplished
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essentially instantaneously with sufficient shearing.
Shearing should be continued until the formulation is
uniform. It is advantageous to predissolve the emulsifier in
the organic li~uid fuel prior to adding the organic liquid
fuel to the oxidizer salt melt or solution. This method
allows the emulsion to form quickly and with minimum
agitation. The emulsifier can be added separately and just
prior to emulsification, however, if desired or if, for
example, the emulsifier would degrade at the elevated
temperature of the fuel. Solid, particulate fuels and/or
oxidizer salts and other ingredients, if any, may be added and
mixed throughout the formulation by conventional means.
Preferably, such solid ingredients are added just prior to
casting. The formulation process also can be accomplished in
a continuous manner as is known in the art. The emulsion once
formed is stable and remains stable even upon cooling to
ambient temperature. The addition of the desiccant and/or
emulsion destabilizing agent causes the emulsion to weaken or
breakdown, which allows the oxidizer salt to crystallize into
a finely knitted crystalline matrix thereby causing
solidification of the composition. The time required for
solidification or casting can be varied by the selection of
desiccant and/or emulsion destabilizing agent, the amounts and
combinations thereof, and the manner in which the emulsion is
formed. The time can vary from essentially instantaneous to
several days. Any temperature-sensitive ingredients such as
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compound explosives preferably are added with the desiccant
and/or emulsion destabilizing agent after the stable emulsion
has cooled to a desired temperature. Cooling equipment can be
used to accelerate the cooling process.
Reference to the following Tables further illustrates the
invention. The examples illustrate the use of various
desiccants (for example, magnesium nitrate, magnesium sulfate
and magnesium perchlorate), desiccants in the aqueous solution
(Examples I, J, K, L and M), various emulsion destabilizing
agents (ethoxylated nonyl phenol, and sodium alkyl naphthalene
sulfonate), and various combinations thereof with various
other ingredients.
The compositions of the present invention can be used in
explosive applications requiring relatively insensitive
blasting agents in large diameters or bulk configurations.
They also can be formulated to be cap sensitive and/or
detonable in small diameters. Because the compositions are
extrudable and/or pumpable when initially formulated, they can
be loaded into containers of various forms for various
applications.
While the present invention has been described with
reference to certain illustrative examples and preferred
embodiments, various modifications will be apparent to those
skilled in the art, and any such modifications are intended to
be within the scope of the invention as set forth in the
appended claims.
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Table I
Composition Ingredients
tParts by Weight) A B C D E F G H
_ _
Emulsion Ingredients
AN 62.62 66.2767.05 55.0750.4068.69 68.40 67.
Sodium nitrate (SN) 15.0516.57 16.6013.6312.48 17.0017.10 16.'
Water 5.85 4.36 4.41 3.62 3.31 4.51 4.50 4.~
Emulsifier (sorbitan 1.23 1.11 1.35 1.11 1.08 1.38 1.54 1.:
monooleate)
Mineral oil 4.87 4045 5.38 4.42 4.32 5.51 4.62 4.
Added Ingredients
Sodium alkyl 4.49 1.93 2.37 1.95 1.79
napthalene sulfonate
Ethoxylated nonyl - - - - - - 0.96
phenol
Magnesium sulfate 5.89 1.93 - - 3.23
Magnesium perchlorate - - 2.84 - - 2.91
Microballoons - 3.38 - 4.63 2 25 - 2.88 3.:
AN prill - - - - 21 14
Ammonium perchlorate - - - 15.57
(AP)
Properties
Density (g/cc) 1.49 ~1.201.49 1.5~ ~1.151.49 1.16 ~1.:
Emulsion Stability >10 >14 >6 >6 >3 >6 >14 >1
(days)
Casting Time (hours) 0.7 ~0.6 0.08 2.0 ~0.4 <96 ~1.5 ~1.(
Detonation ~esults 1
Minimum Booster - 2A/- - _ 2A/40g - ~ 2A/~
(det/fail)
Velocity (km/sec)
Diameter (mm)
150 _ 3.7 _ _ 4.3 _ 5.7
125 - - - - 3.3 _ _ 3
12A = 1709 pentolite booster, 40g = 40g pentolite booster
RHH-OlM
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Table II
Composition Ingredients
( Parts bv Weiqht ) I J ~ L M N
Emulsion Ingredients
AN 64.9963.1663.51 48.05 41.6444.46
SN 16.2515.7915.88 12.01 10.4111.02
Calcium nitrate - - 4~39
Magnesium nitrate6.32 6.20 - 4.67 4.05
Hexamethylenetetramine - - - - - 3.88
Water 4.61 4.43 4.18 3.41 2.95 2.92
Nitric acid - - - - 1.77
Emulsifier (sorbitan 1.44 1.78 1.10 1.94 1.68 0.84
monooleate
Mineral oil 5.79 5.63 4.40 4.47 3.88 3.37
Added Ingredients
Sodium alkyl - - 2.34 - - 1.60
naphthalene sulfonate
Ethoxylated nonyl0.60 0.58 - 0.45 0.39
phenol
Magnesium sulfate - - 4.20 - - 2.79
Microballoons - 2.43 - - - 2.31
AP - - - - - 24.44
PETN - - - 25.0
TNT - - - - 35.0
Properties
Density (g/cc) 1.48 1.20 ~1.50 1.52 1.54 1.18
Emulsion Stability>15 >11 >14 30 30 >12
tdays)
Casting Time (hours) 4.0 6.0 48.0 6.0 6.0 12.0
Detonation Results
Minimum Boosterl
~det/fail) - 3C/- ~ 4-59/~12 _ 2A/40g
Velocity (km/sec)
Diameter (mm)
150 - 4.8 - 6.2 - Det
125 . - - - 5.9 5.~ -
,100 - - - 5.6 5.5
_ _ - s.5 Fail
62 - - - 5.5
_ - - 5.8
38 _ - - 5.3
13C = 340g pentolite booster, 4.5g = 4.59 pentolite booster, ~12 = '12
blasting cap
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