Note: Descriptions are shown in the official language in which they were submitted.
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Low Density Ammonium Nitrate Emulsion Explosive
Field of the Invention
This invention relates to the explosives art, and in
particular, to the production and use of low density
ammonium nitrate-emulsion type explosives.
Description of the Related Art
Various explosive products, such as ANFO (ammonium
nitrate-fuel oil), are widely used in the explosives
industry as a readily available and relatively
inexpensive bulk explosive, and generally comprise a
mixture of about 95% (by weight) porous ammonium nitrate
prills with about 5% (by weight) of a generally liquid,
or liquefiable, hydrocarbon, such as fuel oil. Other
oxidizing salts, such as sodium nitrate, calcium nitrate
and the like may be substituted for a portion of the
ammonium nitrate, and various fuel oils, waxes and the
like may be used for the hydrocarbon component.
In order to modify the handling or performance
properties of an ANFO explosive, and/or to provide water
resistance to ANFO explosives, it is common in the
explosives art to combine ANFO with other materials, such
as, for example, an emulsion explosive to produce an
explosive termed in the industry as Heavy ANFO. Heavy
ANFO is normally used to produce explosives having a
higher loading density than is possible using poured ANFO
alone.
Similarly, ammonium nitrate prills can also be
combined with an emulsion explosive to create a doped
emulsion. The doped emulsion provides a method for
modifying the explosive properties of an emulsion alone.
In order to further control the handling and
performance properties of these types of materials, the
explosives industry is constantly searching for different
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means to control density and product performance for
Ammonium Nitrate (AN)-containing explosive materials.
Summary of the Invention
Accordingly, the present invention provides an
S explosive composition comprising: i) an oxidizer salt
such as ammonium nitrate, optionally in combination with
a fuel oil suitable for producing an ANFO type explosive;
ii) an emulsion explosive matrix; and iii) sufficient low
density material to lower the density of the explosive,
wherein said ammonium nitrate prills are uncoated or have
been pre-coated with up to 2% of a fuel phase by weight
of the formulation.
The low density material is preferably a solid low
density material such as foamed perlite, or a foamed
polymeric material such as foamed polystyrene.
Preferably, the level of the low density material is less
than 50%, by weight, of the total formulation, and more
preferably, is between l and 30%, by weight. More
preferably still, the level of low density material is
between 3 and 15% and even more preferably, between 3 and
7% by weight of the total formulation.
The fuel oil (when present) utilized in the
preparation of the ANFO may be any of the liquid or
liquefiable hydrocarbons generally used in this art. The
amount of fuel oil may, however, vary from standard ANFO
formulation levels in order to adjust the oxygen balance
of the total explosive composition. The level of fuel
oil, when added, is preferably less than 10%, and more
preferably is between l to 6%, by weight of ammonium
nitrate and fuel oil.
The oxidizer salt may, however, be added to the
formulation as a dry particle, preferably in the form of
prills. Most preferably, the oxidizer salt is ammonium
nitrate (AN) in prill form, and in particular, is a
porous, explosives-grade ammonium nitrate (EGAN) prill.
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However, a portion of the ammonium nitrate might also be
replaced by other oxidizing salts known in the industry,
such as sodium nitrate, calcium nitrate and the like. The
level of AN prills in the final explosive composition is
preferably up to 90% by weight. More preferably, the
level of AN is between 60 to 90%, and most preferably
between 70 to 90% by weight.
The emulsion explosive may be any of the emulsion
explosives known in the industry and generally comprises
a discontinuous phase of an oxidizer salt which has been
emulsified into a continuous fuel phase. The level of
emulsion explosive may vary depending on the desired
properties of the final composition, but is preferably
between 3 and 60% by weight of the total composition, and
more preferably, is between 3 and 25%, by weight. More
preferable still, the emulsion explosive comprises
between 5 and 20% by weight, and most preferably, the
composition comprises between 5 to 12% emulsion
explosive, by weight. While the emulsion explosive acts
as a low density blasting agent, it also acts as a
binding agent to aid in through mixing of the AN prills
and the low density material.
The oxidizer salt for use in the discontinuous phase
of the emulsion is preferably selected from the group
consisting of alkali and alkaline earth metal nitrates,
chlorates and perchlorates, ammonium nitrate, ammonium
chlorates, ammonium perchlorate and mixtures thereof. It
is particularly preferred that the oxidizer salt is
ammonium nitrate, or a mixture of ammonium and sodium
nitrate. A preferred oxidizer salt mixture comprises a
solution of 77% ammonium nitrate, 11% sodium nitrate and
12% water, by weight.
The oxidizer salt in the emulsion is typically a
concentrated aqueous solution of the salt or mixture of
salts. However, the oxidizer salt may also be a
liquefied, melted solution of'the oxidizer salt where a
lower water content is desired. It is particularly
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preferred that the discontinuous phase of the emulsion
explosive be a eutectic composition. By eutectic
composition it is meant that the melting point of the
composition is either at the eutectic or in the region of
the eutectic or the components of the composition.
The oxidizer salt for use in the discontinuous phase
of the emulsion may further comprise a melting point
depressant. Suitable melting point depressants for use
with ammonium nitrate in the discontinuous phase include
inorganic salts such as lithium nitrate, silver nitrate,
lead nitrate, sodium nitrate, potassium nitrate; alcohols
such as methyl alcohol, ethylene glycol, glycerol,
mannitol, sorbitol, pentaerythritol; carbohydrates such
as sugars, starches and dextrins; aliphatic carboxylic
acids and their salts such as formic acid, acetic acid,
ammonium formate, sodium formate, sodium acetate, and
ammonium acetate; glycine; chloracetic acid; glycolic
acid; succinic acid; tartaric acid; adipic acid; lower
aliphatic amides such as formamide, acetamide and urea;
urea nitrate; nitrogenous substances such as
nitroguanidine, guanidine nitrate, methylamine,
methylamine nitrate, and ethylene diamine dinitrate; and
mixtures thereof.
Typically, the discontinuous phase of the emulsion
comprises 60 to 97% by weight of the emulsion explosive,
and preferably 86 to 95% by weight of the emulsion
explosive.
The continuous water-immiscible organic fuel phase of
the emulsion explosive comprises an organic fuel.
Suitable organic fuels for use in the continuous phase
include aliphatic, alicyclic and aromatic compounds and
mixtures thereof which are in the liquid state at the
formulation temperature. Suitable organic fuels may be
chosen from fuel oil, diesel oil, distillate, furnace
oil, kerosene, naphtha, waxes, (eg. microcrystalline wax,
paraffin wax and slack wax), paraffin oils, benzene,
toluene, xylenes, asphaltic materials, polymeric oils
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such as the low molecular weight polymers of olefins,
animal oils, fish oils, and other mineral, hydrocarbon or
fatty oils, and mixtures thereof. Preferred organic fuels
are liquid hydrocarbons, generally referred to as
petroleum distillate, such as gasoline, kerosene, fuel
oils and paraffin oils. More preferably the organic fuel
is paraffin oil.
Typically, the continuous water-immiscible organic
fuel phase of the emulsion explosive comprises 3 to 30%
by weight of the emulsion explosive, and preferably 5 to
15% by weight of the emulsion explosive. This level of
the fuel phase may be in excess of the amount generally
used for emulsion explosives only, but may be present in
order to provide fuel for absorption into the AN prills,
where necessary to produce ANFO.
The emulsion explosive also comprises an emulsifier
component to aid in the formation to the emulsion, and to
improve the stability of the emulsion. The emulsifier
component may be chosen from the wide range of
emulsifying agents known in the art to be suitable for
the preparation of emulsion explosive compositions.
Examples of such emulsifying agents include alcohol
alkoxylates, phenol alkoxylates, poly(oxyalkylene)
glycols, poly(oxyalkylene) fatty acid esters, amine
alkoxylates, fatty acid esters of sorbitol and glycerol,
fatty acid salts, sorbitan esters, poly(oxyalkylene)
sorbitan esters, fatty amine alkoxylates,
poly(oxyalkylene)glycol esters, fatty acid amides, fatty
acid amide alkoxylates, fatty amine, quaternary amines,
alkyloxazolines, alkenyloxazolines, imidazolines,
alkyl-sulfonates, alkylarylsulfonates,
alkylsulfosuccinates, alkylphosphates, alkenylphosphates,
phosphate esters, lecithin, copolymers of
poly(oxyalkylene) glycols and poly(12-hydroxystearic
acid), condensation products of compounds comprising at
least one primary amine and poly[alk(en)yl]succinic acid
or anhydride, and mixtures thereof.
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Among the preferred emulsifying agents are the
2-alkyl- and 2-alkenyl-4,4'-bis(hydroxymethyl)oxazolines,
the fatty acid esters of sorbitol, lecithin, copolymers
of poly(oxyalkylene)glycols and poly(12-hydroxystearic
acid), condensation products of compounds comprising at
least one primary amine and poly[alk(en)yl]succinic acid
or anhydride, and mixtures thereof.
More preferably the emulsifier component comprises a
condensation product of a compound comprising at least
one primary amine and a poly[alk(en)yl]succinic acid or
anhydride. A preferred emulsifier is a polyisobutylene
succinic anhydride (PIBSA) based surfactant, which
surfactants are described in Canadian Patent No.
1,244,463 (Baker). U.S. Patent No. 4,822,433 (Cooper and
Baker) discloses emulsion explosive compositions in which
the emulsifier is a condensation product of a
poly[alk(en)yl]succinic anhydride and an amine such as
ethylene diamine, diethylene triamine and ethanolamine.
Further examples of preferred condensation products may
be found in European Patent Publication No. 0,331,306
(published September 9, 1989) and U.S. Patent No.
4,999,062.
Typically, the emulsifier component of the emulsion
explosive comprises up to 5% by weight of the emulsion
explosive composition. Higher proportions of the
emulsifier component may be used and may serve as a
supplemental fuel for the composition, but in general it
is not necessary to add more than 5% by weight of
emulsifier component to achieve the desired effect.
Stable emulsions can be formed using relatively low
levels of emulsifier component and for reasons of
economy, it is preferable to keep to the minimum amounts
of emulsifier necessary to achieve the desired effect.
The preferred level of emulsifier component used is in
the range of from 0.4 to 3.0~ by weight of the emulsion
explosive.
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If desired, other optional fuel materials, hereinafter
referred to as secondary fuels, may be incorporated into
the emulsion explosives. Examples of such secondary fuels
include finely divided solids. Examples of solid
secondary fuels include finely divided materials such as:
sulfuri aluminum; carbonaceous materials such as
gilsonite, comminuted coke or charcoal, carbon black,
resin acids such as abietic acid, sugars such as glucose
or dextrose and other vegetable products such as starch,
nut meal, grain meal and wood pulp; and mixtures thereof.
Typically, the optional secondary fuel component of
the emulsion explosive comprises from 0 to 30% by weight
of the emulsion explosive.
The emulsion portion, or more generally, the complete
explosive composition is preferably oxygen balanced. This
may be achieved by providing a blend of components which
are themselves oxygen balanced or by providing a blend
which, while having a net oxygen balance, comprises
components which are not themselves oxygen balanced. This
provides a more efficient explosive composition which,
when detonated, leaves fewer unreacted components.
Additional components may be added to the explosive
composition to control the oxygen balance of the
explosive composition.
The emulsion explosive component may additionally
comprise a discontinuous gaseous component which gaseous
component can be utilized to vary the density and/or the
sensitivity of the explosive composition.
The methods of incorporating a gaseous component and
the enhanced sensitivity of emulsion explosives
comprising gaseous components are well known to those
skilled in the art. The gaseous components may, for
example, be incorporated into the emulsion explosive as
fine gas bubbles dispersed through the composition, as
hollow particles which are often referred to as
microballoons or as microspheres, as porous particles, or
mixtures thereof.
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A discontinuous phase of fine gas bubbles may be
incorporated into the emulsion explosive by mechanical
agitation, injection or bubbling the gas through the
emulsion, or by chemical generation of the gas ln situ.
Suitable chemicals for the ln situ generation of gas
bubbles include peroxides, such as hydrogen peroxide,
nitrates, such as sodium nitrate, nitrosoamines, such as
N,N'-dinitrosopentamethylenetetramine, alkali metal
borohydrides, such as sodium borohydride, and carbonates,
such as sodium carbonate. Preferred chemical for the in
situ generation of gas bubbles are nitrous acid and its
salts which decompose under conditions of acid pH to
produce gas bubbles. Preferred nitrous acid salts include
alkali metal nitrites, such as sodium nitrite. Catalytic
agents such as thiocyanate or thiourea may be used to
accelerate the decomposition of a nitrite gassing agent.
Suitable small hollow particles for use in the emulsion
explosive, or as the low density material, include small
hollow microspheres of glass or resinous materials, such
as phenol-formaldehyde, urea-formaldehyde and copolymers
of vinylidene chloride and acrylonitrile. Suitable porous
materials include expanded minerals such as perlite, and
expanded polymers such as polystyrene.
In a preferred embodiment, the explosive compositions
of the present invention are formulated using
polystyrene, and preferably, polystyrene which has been
overexpanded in order to have a bulk density of less than
0.04 g/cc. When polystyrene is utilized, it is
particularly desirable that any fuel oil added to the
ammonium nitrate prills, or used in the production of the
emulsion, be compatible with the polystyrene, and not
dissolve the structure of the polystyrene material. For
this application, it is preferable that the explosive
composition be free of fuel oil added to the ammonium
nitrate, and that the emulsion explosive be based on a
vegetable oil, as is described in U.S. Patent No.
5,322,576 issued June 21, 1994. Accordingly, in a
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preferred embodiment, the present invention provides an
explosive composition comprising:i) 70 to 90% by weight,
of ammonium nitrate prills; ii) 5 to 20% by weight of an
emulsion explosive matrix, wherein said emulsion
S explosive matrix comprises vegetable oil as the
continuous fuel phase of the emulsion; and iii) 3 to 15%
by weight of a low density material, which is preferably
foamed polystyrene having a bulk density of less than
0.0~ g/cc, in order to lower the density of the
explosive.
In a further aspect, the present invention also
provides a method for the production of an explosive
comprising mixing of solid particles of an oxidizer salt,
such as porous prills of ammonium nitrate which have been
optionally treated with a fuel oil to produce an ANFO
type material, an emulsion explosive which optionally
contains excess fuel oil, and a low density material such
as perlite and/or foamed polystyrene.
Examples
The invention will now be demonstrated, by way of
example only, by reference to the following examples.
A series of explosive compositions made in accordance
with the present invention were prepared by mixing
together an emulsion explosive, ammonium nitrate, and a
low density material as indicated. The properties of the
resultant explosive were measured, and are presented in
Table 1.
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Table 1
Test No. 1 2 3
Formulation % (by weight): 83 75 84
AN prills
Fuel Oil 2 5 0
Emulsion Expl (a) 10 10 10
Polystyrene 5 - 6
Perlite - 10
Density of AN or ANFO/emulsion0.88 0.9 0.88
mix onl~ (g/cc)
Density with Perlite or 0.5 0.6 0.4
Polystyrene (g/cc)
Velocity of Detonation
(VOD) in m/sec:
0.65cm cartridge - - 2500
15cm cartridge 2,083 1,644
15cm 1,995 Fail
13cm 1,875
(a) - Emulsion explosive comprising:
Examples 1 & 2 - A 70/15/15 mixture by weight of
AN/SN/water as aqueous phase, mixed in a weight ratio
of 93.5 to 6.5 with a mixture of isopar oil and
sorbitan monooleate.
Example 3 - A 69/15/16 mixture by weight of
AN/SN/water as aqueous phase, mixed in a weight ratio
of 91 to 9 with a mixture of vegetable oil (corn oil)
and a PIBSA-based surfactant.
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The results shown in Table 1 demonstrate that usable
explosive compositions can be prepared having reduced
densities over prior art formulations.
Having described specific embodiments of the present
S 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.
