Note: Descriptions are shown in the official language in which they were submitted.
ll)90i3g
The present invention relates to an improved explosive
composition. More particularly, it relates to explosive compos-
itions of the water bearing type generally known in the art as
slurry explosive compositions or slurry explosives or slurried
blasting agents which comprise a fuel and a liquid solvent,
disperser or carrier for said salt. Although the term 'slurry'
is universally applied to such compositions, the degree of
consistency may range from pourable to highly viscous extrudable
gels. The oxidising salt generally comprises nitrates or perch-
lorates of ammonia, sodium, potassium, calcium or barium and
mixtures of any two or more of said nitrates. In the most
extensively used compositions the oxidising salt is ammonium
nitrate alone or in admixture with sodium nitrate.
In slurry explosive compositions the liquid content
is sufficient to maintain a reasonably continuous liquid phase,
which renders the compositions fluid or plastic for direct
loading into boreholes or for packaging in paper or synthetic
plastics wrapped cartridges. As is known, the liquid phase
can be constituted in various ways. Thusj it may consist
mainly of an aqueous solution of oxidising salt but in some
known compositions it comprises an emulsion of water in oil or
it may be a dispersion of oil in droplet form throughout
a thickened aqueous phase. Non-aqueous slurry explosive
compositions are also known wherein a liquid chemical compound
provides the liquid phase.
Thickening agents have been employed extensively to
increase the viscosity of explosive slurry compositions to the
desired degree to prevent segregation of the ingredients and
to improve their resistance to deterioration in wet conditions.
These agents include various flours or~powders of natural
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; polysaccharides (of which guar gum has been the most popular)
and biopolymers such as Xanthan gums. Further improvement in
homogeneity and storage properties of the slurry compositions
has been achieved by chemically crosslinking the thickening
agents with crosslinking agents such as potassium and sodium
dichromates or potassium pyroantimonates which are compatible
with the other components of the explosive slurry compositions.
It is also common practice in the art to aerate -
explosive slurry compositions in order to improve their
sensitivity to initiation by the well known 'hot spot' technique.
Aeration may be effected by mechanical mixing alone but is
generally enhanced by the inclusion of foaming surfactant in
the composition. Other methods are the inclusion of gas filled
spheres of glass or synthetic plastics material or gas generating
compounds in the compositions.
The fuel component is provided in the explosive slurry ;~
composition for oxygen balance and it also enhances the power
and sensitises the composition. The range of fuels is large.
Thus, for compositions for use with heavy priming in large
diameter, coal, carbon black, sulphur, sugar, aluminium,
molasses, starches and various alcohols have been found suitable.
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Sensitising components are included in explosive ~-
slurry compositions to enhance their sensitivity to initiation. ;~
In order to provide more sensitive compositions requiring less
powerful and, therefore, less expensive boosters to initiate
them, more effective sensitising components (which may also be
fuels) are included. Well known sensitisers proposed or used
in this respect have been trinitrotoluene, nitrobenzene, nitric
acid, cellulose nitrate, aluminium, magnesium and boron. Such
sensitisers have disadvantages in that they are solid or liquid
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water-insoluble materials and are difficult to disperse uniformly
and hold in suspension in the slurries. In the case of the
liquid water-insoluble sensitisers, syneresis is liable to
occur in the explosives slurry compositions as finally prepared.
Frequently, the sensitisers have an objectionable odour or
marked physiological properties. Solid sensitisers of light,
finely divided elements are difficult to incorporate in a
homogeneous manner and explosive slurry compositions containing
such components are liable to desensitisation during packaging
operations and while kept in storage.
Liquid water-soluble sensitisers, for example ethylene
glycol monoitrate, are costly and their high costs hinders a
large scale introduction of slurry explosive compositions for
blasting purposes. Consequently, although it is feasible
technically to replace nitroglycerine based explosive compos-
itions with slurry explosive compositions, at present the latter
compositions suitable for use in boreholes of small diameters,
for instance 25 mm, are not commercially viable as replacements
for the conventional nitroglycerine explosives.
The important coneept of this invention is the
development of new sensitising components for slurry explosive
compositions and it is the principal object of the invention
to provide slurry explosive compositions with other sensitising
components in order to minimise or eliminate those disadvantages
encountered in the prior art.
Investigations conducted overseas about six years ago
relating to this subject indicated that most water soluble
fuels imparted better sensitivity than insoluble fuels. It
was postulated that the sensitising action observed with the
use of certain soluble fuels was due to a) solubility of these
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fuels in water, so that both the nitrate and the fuel are in
the homogeneous phase where initiation starts, b) the presence
of a reducing function, and c) lowering of the activation
energy for the initiation reaction.
Recent work by the inventor on the problem of finding
new ways of sensitising slurry explosive compositions and also
reducing the content of known and presently used sensitising
compounds therein because of their high costs has led to promising
developments. He found, inter alia, that fuels such as dimethyl
sulphoxide, for example, could be incorporated in slurry explosive
compositions in small amounts together with small amounts of
additional or auxiliary sensitising compounds and that marked
improvements in sensitivity were obtained thereby in slurry `
explosive compositions. ~
.
Accordingly, this invention provides improved thickened
slurry explosive compositions comprising at least one inorganic ;~
oxidising slat, water, thickening agent, density controlling
agent and sensitising agent, the improvement comprising the use
as the sensitising agent of a homogeneous mixture of a soluble
fuel and an auxiliary sensitising compound wherein synergism
occurs when the soluble fuel and the auxiliary sensitising
compound are mixed together to form the sensiting agent, siad
compound being soluble in the soluble fuel and/or in watar.
The sensitising components of this invention are
compatible with other ways and means of explosive slurry sens-
itisation, such as chemical or mechanical gassing to give
density modifications, the use of light elemental sensitisers
or other sensitisers. Thus, there may advantageously be included
in the composition a foaming surfactant to entrap air during
stirring, or chemical gassing agents such as sodium nitrate or
or thiourea to generate gas in situ or hollow microballoons.
lVS'(~13~
Advantageously, the soluble fuel comprises dimethyl
sulphoxide or other soluble fuels having a reducing function such
as thiourea, sugar and glycerol, or soluble fuels capable of
dissolving substantial amounts of the inorganic oxidising salt(s)
such as formamide, dimethyl formamide and methanol, or mixtures
thereof while the auxiliary sensitising compound comprises
ethylene glycol mononitrate or other sensitisers such as
methylamine nitrate, ethylene diamine dinitrate, methylnitramine,
ethylene dinitramine or any sensitising compound soluble in the
soluble fuel and/or water or mixtures thereof.
Preferably the slurry explosive compositions contain
sensitising agents in which the ratio by weight of soluble fuel
to auxiliary sensitising compound is about from 1:10 to 10:1
and, more preferably, for 1:3 to 3:1.
Slurry explosive compositions of the invention may
comprise, by weight based on the total composition, about from
10 to 75 percent of ammonium nitrate, about from 0 to 30 percent ~
of sodium nitrate, about from 3 to 20 percent of water, about -
from 0.3 to 2 percent of guar gum crosslinked with, based on
the weight of the guar gum, about from 0.02 to 2.0 percent
of crosslinking agent, (such as, for example, potassium ~-
pyroantimonate, zinc chromate or dichromate of sodium or pota-
ssium), about from 0.1 to 10 percent of surfactant/stabiliser
paste to generate and retain stabilised bubbles throughout the
composition, said composition being sensitised by about from
5 to 30 percent of a sensitising agent, which is a homogeneous
mix ure of about from 1 to 10 percent soluble fuel and about
from 1 to 20 percent of auxiliary sensitising compound.
Additional ingredients may be added such as are
known or used in the prior art and other convenient fuel
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materials including aluminium powder, urea and flours of
cellulosic materials.
In the following examples, wh~ich illustrate this
invention, the percentages and ratio~ are by weight unless
otherwise indicated. The Table shows three slurry explosive
compositions, each of which had incorporated therein an amount
of 7 percent of sensitising agent. It will be observed that ~- -
the first composition contained dimethyl sulphoxide, the
second composition contained ethylene glycol mononitrate and
the third composition contained a mixture of 3 percent of ~-
DMSO and 4 percent of EGMN. It will be observed further that
the first and second compositions failed to initiate even
with the aid of a booster whereas the third composition was - ;~
initiated by a detonator only. A type 6D detonator has a base
charge of 350 milligrams of pentaerithritol tetranitrate (PETN)
and the "Anstart" (Registered Trade Mark of AE & CI Limited)
brand of booster has a base charge of 1.35 gm. of PETN. This
significant test result clearly indicates the synergistic
effect of the two components in the sensitising agent.
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TABLE
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EXAMPLE 1 2 3
_
Dimethyl sulphoxide (DMSO)7.00 Nil 3.00
Ethylene glycol mononitrateNil 14.00 8.00
liquor* (EGMN) (=7% EGMN) (,4% EGMN)
Water 8.00 7.00 8.00
Ammonium nitrate (AN) 62.33 51.63 55.73
Sodium nitrate 15.00 15.00 15.00
Aluminium (atomised) 6.00 6.00 6.00
Wood meal Nil 4.70 2.60
HP-l Guar gum 0.50 0.50 0.50
Potassium pyroantimonate 0.02 0.02 0.02
Surfactant/stabiliser ..
paste** 0.65 0.65 0.65
Acetic acid/sodium acetate ~ -
buffer 0.50 0.50 0.60
Density g/cm3 1.17 1.17 1.17
Minimum initiator : .
(unconfined) >6D ~ Anstar 76D ~ Anstart 6D
Temperature 28C 28C 28C
Diameter 25 mm 25 mm 25 mm
* EGMN 50%
AN 28%
Water 18%
Glycol 4% :-
** paste acutally used was a mixture of 3.3 parts ethoxylated
ammonium lauryl sulphate to 1 part of a blend of C20 - C22
aliphatic amines.
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