Note: Descriptions are shown in the official language in which they were submitted.
AECI 610
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"Emulsion Explosive ContaLning Particulate Insoluble Bentonite" ~
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THIS INVENTION relates to an explosive. lt relates in particular to the
manufacture of an emulsion explosive comprising a discontinuous phase
which forms an oxidizing salt-containing component and a continuous
5 phase which is immiscible with the discontinuous phase and which forms a
fuel component.
'""''':
Such explosives, when the oxidizing salt-containing component contains
water and is in the form of an aqueous solution, are known as
'water-in-fuel' emulsions, and when Ihe oxidizirg salt component
10 contains little or no water, they can be regarded as 'm;it-in-fuel'
emulsions.
' .;
According to the invention, in the manufacture of an emulsion explosive `~
comprising a discontinuous phase which for2s an oxidizing
salt-containing component and a continuous phase ~ich is immiscible ;
15 witll the discontinuous phase and which forms a fuel component, there is 5
provided a method of thickening or increasing the viscosity of the
emulsion which comprises dispersing insoluble parti~ulate benton]te in ;
at least o~e of the components of the emulsion.
The bentonite may be added to the emulsion formed after admixture of
20 s~id components, in a proportion o~ from about 1,0 tc about 5,0% by mass ` -~
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based on the emulsion mass. The Applicant has found that the bentonite
is thereby dispersed through the emulsion withou~ dissolving in eit~er
of ~he c~nponents, and without causing crystallization.
The bentonite may be swellable sodium bentoni~e which is composed
largely of the mineral montmorillonite. It may be of the so-called USA
tight-spec type having a degree of dry particle fineness as follows:
90% by mass minimu~ finer than US Sieve No. 40 and 10% by mass maximum
finer than US Sieve No 200. In other words, at least 90~ by mass of the
bentonite particles may have a particle size less than 425 microns and
15 at the most 10% by mass of the bentoni~e Farticles may have a particle size
less than 75 microns. The average particle size of the bentonite
particles may be from about î5 microns to about 425 microns, preferably
from about 75 microns to abou-t 350 microns.
The sodium bentonite may be that which is commercially aYailable in
powder form under the trade name h~-80*VOLCLAY h~STERN BENTONITE-l~T
from The AmeTican Colloid Company, and which has a water content of
between 5 and 10~ by mass, a dry particle fineness of 10% by mass
maximum retained on US Sieve No. 40 and 10% by mass maximum passing US
Sieve No. 200, and a wet particle ~ineness of at least 94% by mass being
finer than US Sieve No. 20~ and at least 92% by mass being finer than US
Sieve No. 325.
The bentonite may be dispersed in the emulsion by admixture of the
powder with the emulsion in a low shear blender.
.
The discontinuous phase may comprise at least one oxidizing salt
; 30 selected from the group cons;sting of ammonium nitrate, al~ali me~al
f
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nitTates, alkaline earth metal nitrates, ammonium perchlora~e, alkali
metal perchlorates, and alkaline earth metal perchlora~es.
The discontinuous phase may comprise ammonium nitrate with at least one
further compound selected from the group consisting of oxygen-releasing
salts and fuels which, together with the ammonium nitrate, forms a melt
which has a melting point which is lower than that of the ammonium
nitrate. Said further compound may be sodium nitrate, calcium nitrate,
urea, urea derivati~es such as thiourea, or the like. The discontinuous
phase may in certain cases comprise water, which is kept to a minimum to
avoid wasted energy arising from steam generation, but which is employed
to facilitate melting/dissolving of the oxidi~ing salt component to
avoid excessive high processing temperatures during formation of the
base emulsion.
The fuel component of the emulsion may fonn from 2 tO 25% by mass of the
emulsion, preferably about 3 to 12% by mass.
The fuel of the fuel component will be immiscible with and insoluble in
water. Preferably, the fuel of the fuel component is non-self-explosive
and is selected from at least one member of the group consisting of
hydrocarbons, halogenated hydrocarbons and nitrated hydrocarbons.
Typically, said fuel comprises at least one wax selected from the group
consisting of paraffin waxes, microcrystalline waxes and slack waxes,
and it may comprise at least one member of the group consisting of
mineral oils, fuel oils, lubricating oils, liquid paraffin, xylene,
toluene, petrolatum and dinitrotoluene.
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The fuel may comprise an emulsifier or a mixture of suitable
emulsifiers. The fuel component may thus comprise at least one
elnulsifier selected from the group consisting of sorbitan sesquioleate,
sorbitan monooleate, sorbitan monopalmitate~ sodium monostearate, sodium
tristearate, the mono- and diglycerides of ~at-forming fatty acids, soya
bean lecithin, derivatives of lanolin, alkyl benzene sulphonates, oleyl
acid phosphate, laurylamine acetate, decaglycerol decaoleate,
decaglycerol decastearate, 2-oleyl-4,4'-bis(hydroxymethyl~-2-oxazoline,
polymeric emulsifiers containing polyethylene glycol backbones with
fatty acid side chains and derivatives of polyisobutylene succinic
anhydride.
The emulsifiers act as surfactants and stabilizers to promote the
- formation of the emulsion and to resist crystallization and/or
coalescence of the discontinuous phase.
The method may include the step of dispersing a density-reducing agent
in the emulsion to form an emulsion having a densi~y of from 1,10 to
1,15 g/cm3 at 25C.
The density-reducing agent may be selected from the group consisting of
microballoons, microspheres and gas bubbles. ln one embodiment, the
eventual emulsion may thus include glass microballoons, microspheres of
polymeric material or another form of density-reducing agent, to provide
the emulsion with the final density of 1,10 to 1,15 g/cm3 at 25C. The
emulsion may then comprise up to about 1~% by mass of glass
microballoons (eg C15/250*glass microballoons available from 3M South
Africa (Pty) Limited) or microspheres of a polymeric materi~l (eg
EXPANCEL 642 DE*microspheres available from KemaNord AB, Sweden) 9 which
,~ * Trade Mark
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can further act to sensitize the explosive. Al~hough the mass of
microballoons or microspheres included may be up to 10%, it is
preferably less than 4,5~ by mass, based on the mass of the emulsion to
which they are added. In anot~ler embodiment, the density-reducing agent
may comprise air bubbles in the emulsion. The bubbles can then be
mechanically induced eg by physical mixing or blowing, and/or chemically
induced, eg by a chemical ~oaming agent such as sodium nitrite added to
the emulsion.
,
The inYention extellds to an emulsion explosive whenever m~nufactured ~ ~;
accordin~ to the method déscriDed above. ~- -
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The invention will now be described by way of example, with reference to
the following non-limiting Examples.
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Cartridged water-in-oil emulsion explosives were prepared having the
following compositions, in which all units are expressed as percentages
or. a mass basis:
Constitue~lt Sample 1 Sample 2
Ammonium nitrate 68,60 65,98
Sodium nitrate 12,81 12,32
Thiourea 0,1 -
l~ater 10,11 9,73
P9S*Oil 0,97 0,93
Crill 4*(sorbitan monooleate emulsifier) 1,36 1,31
Paraffin Wax (Aristo~ ~ 1,98 1,90
Microcrystalline Wax (BE SQUARE Amber)* 1,9g 1,90
Bentonite 2,00 2,00
Sodium nitrit~ ~20% m/m aqueous solution) 0,09
3M B23/500*Microballoons ^ 3,93
TOTAL 10G,00 100,00
Cold Density (g/cm3) 1,15 1,15
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The P95* (trade name) mineral oil was obtained from BP South
Africa (Proprietary) Limited, and the Crill 4* (trade name)
from Croda Chemicals South Africa (Proprietary) Limited. The
paraffin wax was Aristo* (trade name) wax obtained from Sasol
Chemicals (Proprietary) Limited, and the microcrystalline wax
was BE SQUARE Amber 175* (trade name) obtained from Bareco
Inc. USA. The microballoons were 3M B23/500* (trade name)
glass microballoons obtained from 3M South Africa
(Proprietary) Limited. The bentonite was MX-80*VOLCL~Y
WESTERN BENTONITE-13T (trade name) obtained from American
Colloid Company, and typically having the following chemical
analysis: Si02 60,0-62,0~ m/m; Al2 03 21,0-23,0% m/m; Fe2 3
3,0-4,0% m/m; MgO 2,0-3,0% m/m; Na20 2,0-3,0% m/m; GaO ~-
0,1-0,7% m/m; X20 0,4-0,5% m/m; and having a pH value of
8,5-10~0.
The amount of water given includes the water used to make up
the sodium nitrite solution.
The emulsion explosives were prepared by forming a premix o~
water, ammonium nitrate, sodium nitrate, and thiourea at about
80 to 90C, and a second premix of the microcrystalline wax,
paraffin wax, P95 oil and Crill 4 at about 70 to 80C. The
first premix was then slowly added to the second premix with
agitation to form a base emulsion. The bentonite was
therea~ter admixed with the base emulsion in a low shear
blender for about 1 minute to provide a thickened emulsion.
Samples 1 and 2 were prepared by respectively dispersing the
sodium nitrite or the microballoons in the base emulsion in a
blender at normal elevated working temperatures, followed by
cartridging and rapid cooling. Comparative samples, identical ; ~
30 to Samples 1 and 2 save that they did not contain bentonite, ~`
were also made up.
*Trade Mark
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Samples 1 and 2, with and without the bentonite, were tested according
to the Stanhope cone penetrometer method (with 150 g cone), and the
results obtained are set out in Table I.
TABLE I :~
LE - PENETRAlI~ -
without bentonite ~ with benton
(i) Temperature 30UC
Sample 1 22,5 18,0
Sample 2 13,5 7,8
~ii.) Teme~ ature 50C
Sample 2 19,4 16,4 ~ :
(iii) Temperature 60C
Sample 2 23,4 17,3
The viscosi~y of Sample 2, with and without the bentonite, was measured
at elevated temperatures, and the results are set out in Table II.
TABLE II
Temperature Viscosity
~ample 2 without Sample 2 with
bentonite .bentonite
26 800 76 800
17 600 19 600
7 600 13 120
Sample 2, with and without the bentonite, was also tested for minimun
initiation ~MI) and velocity of detonation CVOD) at 40C, and the
results are set out in Table III. Table III also sets out the results
of tests for MI and VOD at 40C of a further sample ~ermed Sample ~,
, . . .
; . .. . .
f. ~ ~
,~. :- ` , ` .
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,
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which is a formulation essentially similar to Sample 2 but which
contains 4% by mass of the bentonite based on ~he mass of the emulsion.
In Table III, ~M' indicates a misfire, and '3D', '4D' and 'SD' indicate
that the explosive could be detonated with a detonator containing 45mg,
90mg, and 180mg pentaethyritol tetranitrate respectively.
TABLE III
SAMPLE Detonation Characteristics at 40C
Initial After 4 months A~`ter 6 months
Ml VOD MI V~ MI VO~
~km/s) ~km/s) ~km/s)
Sample 2 3D 4,9 SD4,7 M8D
(without
` - bentonite) - - - -
Sample 2 3D 4,7 4D` 4,7 5D 4,9
(with 2%
bentonite)
Sample 3 3D 4,8 SD4,7 M8D
(4~ bentonite)
-
Sample 2, with and withcut bentonite, was tested for susceptibility to
shock crystallization, and the results are set out in Table IV
(Temperature Rise on Shocking) and Table V ~Bubble Energy after
ShocXing). Temperature rise on shocking was measured by placing a
thermocouple in the centre of a cartridge suspended vertically at 6,7 m
below the surface of water. A 150g booster was fired at the same depth
at a distance of 2,8m from the cartridge and the ~esultant temperature 1
rise due to crystallisàtion was recorded. The average of three results
is given in Table IV . Bubble energy after shocXing was measured by
firing a 150g booster at varying distances from five cartridges
~ 3 ~ J
suspended vertically at a wa~er dep~h of 6,7m The cartridges were
detonated 13 seconds later ~ld their bubble energy recorded as given in
Table V. ~he same method of shocking was use~ ~or Sample 2 ~without
bentonite) and Sample 2 ~wi~h bentonite).
TABLE IV :~ :
TEMPERATURE RISE ON SH0CKING -~
SAM~L~ Iemperature RlseI`ime taken to Keach
(C) hlaximum Temperature
~S) ' '
Sample 2 2'~,3 360
(without bentonite)
Sample 2 21,0 360 :-.~with bentonite)
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- TABLE V - . -;
BUBBLE ENER~Y AFTER SH0CKING
SAMPL~ Dist~ce from Booster~ubble Energy ::~
(m) ~MJ/kg)
Sample 2 - 2,10
(without bentonite3 5 1 50
2 1,45
1,8 - 1?40
1,75 Mlsfire
Sample 2 - 2,10 . ~
(with bentonite) 5 1,55 ~ :
2 1,45
1,8 1,40 : : `
1,75 Misfire ~ ~
.' ~;`.'.',''''~"~
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Without wishing to be bound by theory, the Applicant believes ~hat thie
desired increase in viscosity on addition of bent~nite to emulsion
explosives is obtamed by the bentonite acting on components sudl as the
wax on cooling, thereby causing swelling of these camponents (indicating
modification of the cTys~al structure thereof) and hence thickening of
the emulsion.
The increased emulsion viscosity pro~ides advantages such as higher
degree of gas or air bubble retention and hence longer shelf life.
The addition of bentonite to emulsion explosives causes an increase in
rigidity at all temperatures, but the resistance to softening at high
temperatures is increased considerably, as seen from the ~iscosity (see
Table II)-and cone penetration values (see Table I).
