Note: Descriptions are shown in the official language in which they were submitted.
lO~ S
CIL 574
This invention relates to gelled or thickened
aqueous slurry explosive blasting compositions of improved
stability. More particularly, the invention relates to
thickened slurry explosives containing sensitizing air or gas
bubbles which resist migration or coalescence.
Slurry explosive compositions are usually formulated
from water, at least one oxygen-supplying salt, fuel, a thickener
and optionally, a thickener crosslinker. The oxygen-supplying
salt most frequently used is ammonium nitrate, often accompanied
by sodium and/or calcium nitrate, and less often by other
nitrate salts, or perchlorates, or chlorates. The ~uel may
be liquid or solid particulate, and may be soluble or insoluble
in water. Both natural gums and synthetic materials may be
employed as thickeners, while borates, chromates and anti-
monates are frequently employsd as crosslinking agents.
Slurry explosive compositions may also contain self- ~ `
explosive sensitizers ~uch as particulate TNT which are in-
soluble in water. Paint-fine aluminium is also used for sen-
sitizing purposes. These sensitizers can contribute all or
part of the fuel required for the composition. Slurry explosives
also rely frequently for their sensitivity on the presence of
small air or gas bubbles within the matrix to create "hot spots"
for shocX initiation. These bubbles reduce the density of the
slurry from the unaerated range of 1.4 to 2.0, to as low as 0.5.
The presence and efficiency of air or gas bubbles is
particularly important in large-diameter slurries which contain
- 2
-
~1)8~965
no self-explosive sensitizer and thus rely nearly completely
on the bubbles for generation of initiating reaction sites
following passage of the shock from a primer charge, It is
believed that there is an optimum size for the bubbles and that
they must also be stabilized to resist size changes and loss
from the slurry. Bubble loss and coalescence can usually be
controlled by achieving a sufficiently high viscosity in the -'
slurry using thickening and crosslinking agents. However,
the viscosity of a composition does not generally affect
the rate of gas transport through the liquid phase of the
slurry so bubble sizes can still change by diffusion of dis-
solved air or gas in a mechanism known as "Ostwald ripening".
The average size of the bubbles increases with time because of
this phenomenom, resulting in lower velocities of detonation
and eventually complete failure of the composition to detonate.
A particularly severe condition for bubble stability -
~
occurs during the pumping of an aerated explosive into packages '
or boreholes. The high shear generated within the pump will
frequently de~ensitize the explosive by coarsening the bubble
stru^ture or even causing the bubbles to migrate completelyout of the slurry.
It is often desirable to prepare a prethickened
liquor of wataE and some dissolved salts which liquor is used
for the manufacture of an explosive slurry by the addition `,~
thereto of other ingredients. This procedure is used
to save time during the mixing procedure because hydration , ~ ;
9~5
of the thickener can be slow in a fully formulated slurry.
Natural guar gum is the thickener of choice for slurry explosive
liquors and compositions. The thickened liquors are normally
stored at their temperature of use which is often above 50C.,
leading, particularly with natural guar gum, to degradation of
the thickening agent and lowering of viscosity with time.
Hence more natural guar thickener may have to be added at inter-
vals, which addition is difficult to incorporate efficiently and
also frequently inconvenient logistically.
Calcium nitrate-containing compositions present special
thickening problems because of the effect of the calcium ion on
natural guar gum. In thepresence of large amounts of Ca2~,
the rate of hydration of the guar is retarded, and when fully
thickened, the viscosity of the solution is very high. This
can cause problems in mixing and pumping the slurry. If the
thickener level is lowered to accommodate the processing re-
quirements, the final gel strength and water resistance after ` ;~
crosslinking is frequently unacceptable. It is therefore par-
ticularly important with C~ containing compositions to choose
a thickener which can reconcile these conflicting re~uirements.
Problems are also sometimes encountered with the
efficient crosslinking of thickened slurries. If crosslinking
is too slow with a bulk slurry when pumped into a water-filled
borehole, losses of the explosiva into rock fissures or leaching
of the soluble ingredients, can occur, thus leading to failure
of the explosive. If crosslinking is too fast, it is usuaIly
- 4 -
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1~8~965
impossible to mix in the crosslinker homogeneously. Some areas
of the slurry are not crosslinked, leading to a water leaching
problem, while other parts contain concentrated pockets of cross-
linker, which can lead to syneresis and chemical degradation of
the slurry. The thickener level is often limited in range,
being a compromise between ease of mixing and pumping, and ;
having sufficient viscosity to suspend the ingredients and
prevent the escape of air bubbles. Also the crosslinker level
is often limited in range because sufficient needs to be added
to give a satisfactory water resistant gel, but not enough to lead
to syneresis. Hence the possibility of being able to select
a thickener, or blend of thickeners, to give a convenient cross-
linking rate can be most advantageous.
It has been discovered that the use of a blend of
natural or unmodified guar and hydroxypropyl-modified guar as
the thickening agent in explosive slurries provides many ad-
vantages over the use of unmodified guar alone. While the
discovery has particularly utility for use in slurry explosives
devoid of any self-explosive sensitizer and used in large
diameter bulk-loaded boreholes, use of the blended thickeners
also has application in slurries containing insoluble explo-
sive sensitizers and/or small amounts, up to ten percent by
weight, of a soluble sensitizer and used in smaller charges.
Guar gum is classified in chemical terms aq a
galactomannan, or a high molecular weight carbohydrate polymer
or polysaccharide made up of mannose and galactose units linked
- 5
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together in the manner shown in the structural formula below.
CH20R CH20H
HO RO _
i I 0~ H / I ~ H
E ~ /~ )H
H H H
O
~H2 CEI20H 1H2 CH20H
~ ~l \ 0 H ~ o ~ ~ 0 H~
With hydroxypropyl-modified guar, R is -CH2CH(CH3)0H,
or polymers thereof, and the number of moles per hexose unit
of the substituted R may vary from about 0.1 to about 3. The
particular hydroxypropyl guar used in the examples hereinafter ;
had a molecular substitution ratio of about 0 4 . The molecular
weight of guar gum can vary from about 50,000 to 250,000 depending
on the method and conditions of refining and modification.
The following Examples and Tables further illustrate
the improved bubble stability of the explosive slurry compo-
sitions of the invention. In all examples the proportions
of ;ngredients is expressed as percent by weight unless other-
wise indicated.
EXAMPLE 1
A typical aqueous slurry explosive composition used
in large diameter charges was prepared comprising 13% water,
76% salts, 10% fuel comprising: 6% sulphur, 3.5% fuel oil, .
0.5% carbonaceous material, and 0.6% thickener. Four separate ~ -
,: .: . ~
- 6
~81965
mixes were prepared using various thickener combinations as
shown in Table I, below, and each mix was passed through a
typical mechanical pump used in slurry operations. The den-
sities of the mixes were measured at various time intervals, the : .
results being shown in Table I.
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From the above data it is seen that as little as
1 part in 6 of hydroxypropyl~ guar will stabilize density and
bubble structure during pumping The third experiment was
particularly severe, since the temperature fell well below
the liquor fudge point of 40C.
EXAMPLE 2
Eight batches of explosive slurry similar to
those described i~ Example 1 were prepared using a 1:1 blend -
of straight guar gum and hydroxypropyl-modified guar gum,
while eight indentical batches were prepared using straight .
guar gum alone. The sixteen slurries were stored overnight
at 50C. in an uncrosslinked state. The results are shown
in Table II
TABLE II
_, :
As made After S~oraqe Change
Original mean Mean density in bubble
density rise structure
. .. ..
Blended guar 1.10 0.02 Little change,
bubbles slightly
laxger but even
. distribution
maintained
Straight guar
alone 1.14 0.07 Greater change,
bubbles much
larger on
average and less
even distribu-
9~s
EXAMPLE 3
The explosive slurries of Example 2 were cross-
linked and stored for 1 week. Six inch diameter cartridges
of each slurry type were then detonated at about 5C. un-
confined using a 1 lb. pentolite primer. Of the mixed guar
cartridges, five detonated with velocities of 3 km/sec. or
greater, while only two cartridges made with straight guar
alone gave such useful velocities of detonation. The greater
reliability of explosive slurries made using a blend of
straight guargum and hydroxypropyl-modified guar gums was
thus demonstrated.
EXAMPLE 4
A typical liquor used in formulating aslurry
explosive was prepared comprising 43% by weight ammonium
nitrate, 52% by weight calcium nitrate and 5% by weight ~ ~
water. To thicken quantities of this liquor, various guar ~ -
gum combinations were added as shown in Table III and the
viscosities of the mixture were measured at the various time
intervals shown in the Table. The guar thickeners were ~ `
hydrated at 50C. for 1 hour ~nd stored at 70C. After one ~ ~
week the samples were crosslinked by adding 0.5% by weight ~- ; ;
of sodium dichromate at 45C. and the gel strengths were
measured using a viscometer at 5 rpm with Helipath stand
and 0.195" T-bar
- 10 - ' ~::
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~(~8~5
TABLE III
G u a r Viscosity cps Gel
Natural Hydroxy- ¦ Strength
propyl 1 hour 1 day 7 days
. _ . .,1.0% _ 250 86,200 71,000 41.8
0.8% 0,2% 1000 90,500 89,000 66.9
0.5% 0.5% 2700 79,400 87,000 59.2
_ 1.0% 7000 30,600 30,000 _
Examination of the results if Takle III shows that
natural guar alone hydrates very slowly and tends to produce
lowered viscosity after only 7 days. Gel strength is low. -
The use of modified guar alone produces faster hydration
but low final viscosity. The blended guaxs produce excellent
retention of viscosities and high gel strength.
EX~MPLE 5
The rate of crosslinking of slurries such as are
described in Examples 1-3 can be varied by choosing thickened
blends having different properties of straight and hydroxy-
propyl-modified guar gums. The examples tabulated below
were crosslinked using 0.5% of a solution of sodium dichromate
(65%) in water (35%, by weight) and the time interval measured
until a self-supporting gel was obtained:
TABLE IV
. _ _ . .
Guar Blend Gellinq tim
1.0% straight guar alone 5 1/2 mins.
0.8% " " + 0.2% HP guar 12 1/2 "
0.5% " " + 0.5% " " 20 " ~-
- 11 - . , ~ :
~L~819~5
The blended guar thickener used in the slurry
explosive compositions of the present invention is present
in an amount of from 0.2% to 2 0%, pre~erably from 0 4% to
1.4% by weight of the total slurry composition. The blend
comprises from 15 to 85 parts by weight of unmodified guar
to 85 to 15 parts by weight of hydroxypropyl modified guar.
A small amount, up to 1.0% by weight of the total composition,
of crosslinker may also be present Slurry explosive compo-
sitions employing the blended guar thickener may contain up to
76% by weight of inorganic salts, up to 25% by weight of water ~ -
up to 30% by weight of sensitizer and up to 40% by weight of
fuel. Up to 27% of the inorganic salt may comprise calcium
nitrate
EXAMPLE 6
An aqueous slurry explosive composition typical
of the type used in large diameter blasting charges was pre-
pared comprising 62.3% ammonium nitrate, 13.4% sodium nitrate, ;
0.3% zinc nitrate, 13.2% water, 3.5% fuel oil, 6.0% sulphur,
0.5% sodium lignosulphonate, 0.6% thickener, 0.060/Oferrous
sulphate and 0.14% sodium nitrite (gassing agent), all quanti-
ties being percent by weight. This composition containing
various thickener combinations as shown in Table V below, was
passed through a L.5 cm diameter x 25 cm long nozzle at the
end of a laboratory scale blowcase having 10 cm bore. Before
each pass the blowcase was filled with the slurry. Blowcase
extrusions simulate the shear effect on slurry when it is pump-
ed through hoses to fill boreholes or during cartridging
operations. The results are recorded in Table V below.
~ 12
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The results in Table V demonstrate that slurry explo-
sives thickened by means of a blend of unmodified guar and
hydroxypropyl modified guar maintained density and
bubble structure and also showed reduced bubble growth when
compared to other thickening systems. It can be noted that
the use of unmodi~ied guar alone or with starch provided little
density or bubble stability. In all cases, viscosities were
measured using Brookfield RVT viscometer with No, 6 spindle
at 20 rpm.
EXAMPLE 7
A slurry explosive composition similar to that of
Example 6 but devoid of sulphur was manufactured using standard ~-
slurry mixing procedures. Various batches containing different ~
,
thickener combinations were examined and fired after periods ~-
of storage. The results are recorded in Table VI, below: `
- 14 -
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1~31965
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The results shown in Table VI demonstrate that
the use of mixed guars provide good density and bubble sta-
bility when stored uncrosslinked at 50C. It can be noted
that the sample containing only unmodified guar failed to
shoot after 8 days storage, due chiefly to poor bubble sta-
bility and a resultant loss in sensitivity.
To demonstrate the improved effect of the use of
a mixed guar thickening system in slurry explosive composi-
tions also containing sensitizing material including self-
explosive sensitizers, a series of sensitizer-containing
compositions were prepared and tested. Suitable additional
sensiti~ers compatible with the mixed thickener system of
the invention comprise, for example, particulate organic -
explosives such as PETN, T~T and the like, particulate
light metals such as air atomized aluminium, organic
nitrates, such as alkanolamine nitrates and lower alkyl-
amine nitrates. Generally from 10% to 30% of sensitizer -~
may be employed. ~ -
EXAMPLE 8
Two TNT-sensitized compositions were prepared
having the following ingredi~nt mix, the quantities shown
being percent by weight:
Composition Composition
"A" "B"
Ammonium nitrate 44.3 44.8
Sodium nitrate 8.7 8.8
Zinc nitrate 0.3 0.3
Water 14.0 14.1
Pelleted TNT 20.0 20.0
Atomized aluminium lO.0 10.0
Ammonium lignosulphate 0.5
- 17
': ; , - : .
1~8196S
Composition Composition
"A" "B"
_
Thickener 0,5 0,5
Ethylene glycol 1.6 1,6
Sodium nitrite 0.1 0.1 :~
Both compositions were tested in blowcase tests
as detailed in Exampl.e 6. The results are recorded in :
Table VII, below~
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965
From Table VII it can be seen that the use of the
mixed guar thickener system provides particular stability and
resistance to shear (during extrusion) as evidenced by density
and bubble structure results It can be noted that Composition
B, devoid of any lignosulphonate had somewhat poorer bu`bble
stability after blowcasing; however, the use of mixed guars
(Test 4) even in the absence of lignosulphonate retained
stability.
EXAMPLE 9
The following slurry explosive composition useful
in large diameter blasting charges was prepared by standard
mixing methods, tha quantities shown being percent by weight:
Ammonium nitrate 56.9~!
Calcium nitrate 23.0
Zinc nitrate 0.3
Water 9.8 ~
Ammonium lignosulphonate 0.5 ~.
Hydroxypropyl guar 0 2
Unmodified guar 0.3
Starch 0.5 ~ -
Fuel oil 5.2
Ferrous sulphate 0.06 .
Atomized aluminium 3.0 ;:~
Sodium nitrite 0.14
Sodium dichromate 0.1
This composition additionally containing two different
types of low viscosity guar as shown in Table VIII below, were
subjected to blowcase testing as described heretofore. The ~.
results are given in Table VIII, below: . :
- 20 -
. : , . -.:
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i . .-....... . . .. ,:
'' ; ,, ' . , ' ' ', . ~, ,
T A B L E VIII
,
Thickener /O/W Test 1 ~ Test 2
.
Unmodified Guar 0.2 _
Hydroxypropyl Guar _ O 2
(low viscosity)
Blowcase (Viscosity at start 31,000 cps 33,500 cps
experiment(Temperature
10 passes ( C at start 44 50
(Density at start 1.00 1.03
(Bubble structure
( at start Fine, even Fine, even
(Temperature C
(after 10 passes 35 37
(Density after
( lO passes 1 03 l.01
(Bubble structure
(after 10 passes Coarse, few Unchanged from
fine bubbles, before blow-
many large casing
bubbles ca 300J~
. _ . _ _ ~, .
After storage (Density 1.10 1 08
for 12 days (
at ambient, (Shooting at DET with 40 g. DET with 9 g
crosslinked (18-19C pentolite at Detaprime at
slurry in 3" ( -3.8 km/s 3 8 km/s
diameter ( Fail with 20 g Fail with 5 g
cartridges ( pentolite Detaprime
(Shooting at
(5C Fail with DET with 80 g
( 160 pentolite pentolite at -
( 3.5 km/s
( Fail with 40 g
( pentolite
. . _ .. __ .
*Brookfield RVT viscometer, spindle No. 6 at 20 rpm.
From Table VIII, Test 1, it is seen that bubble
structure is substantially coarsened in the absence of
modified guar Also, sensitivity after storage is improved
when some modi~ied guar is employed.
- 21
.
f;5
EXAMPLE 10
A slurry explosive composition sensitized with
ethanolamine nitrate, a soluble organic explosive salt,
was prepared using standard mixing procedures and comprising
the following ingredients, the amounts shown being in percent
by weight. ~:
Ammonium nitrate 63.8
Sodium nitrate 13.0
Zinc nitrate 0.3
Ethanolamine nitrate 6.0
Water 11.1
Fuel oil 4.6
Ammonium lignosulphonate0.5 ~ :
Thickener 0.5
Sodium nitrite 0.1
Sodium dichromate 0.1
Samples of the composition containing different ~ :
thickening systems were blowcase tested as described hereto-
fore. The results are shown in Table IX, below:
.: , . . :
- 22
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965
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9~5
From the results in Table IX, it is seen that in
the absence of a mixed guars thickening system, density was
unstable. After storage, a density rise occurred in the
absence of any hydroxypropyl guar, demonstrating an un-
stable bubble structure.
EXAMPLE 11
A slurry explosive composition sensitized by
means of finely divided aluminium was prepared using standard
procedures and comprised the following ingredients, the
amounts shown being percent by weight:
Ammonium nitrate 65 0
Sodium nitrate 7.6
Water 14.0
Sodium acetate (buffer) 0.1
Gilsonite 1.1
Atomized aluminium 3.8
Paint-fine aluminium 3.8
Ethylene glycol 3.8
Thickener 0.8
Pot. pyroantimonate 0.04
Samples of the composition containing different
thickener systems were subjec-ted to blowcase testing as
described heretofore. The results are given in Table X,
below:
' ':
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The results in Table X show improved stability
of the density of the compositions with the use of a mixed
guar thickener system.
DONALD G. BALLANTYNE
PATENT AGENT
- 27
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