Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to foamable, explosives containing compositions.
Liquid explosive combinations as colloids, suspensions or solutions are well known
in the art and the advantages of small bubbles in such liquid combinations are also
well known. Thus, in U.S. Patent Specification No. 3582411 it is suggested that the
5 inclusion of a large number of small bubbles in a liquid explosive combination affords
active reaction centers which assists propagation of the detonation reaction whilst in
U.S. Patent No. 35865S3 the compositions disclosed, being liquid explosive
combinations with gas bubbles therein, are described as being highly brisant with high
detonation velocity and capable of being produced in a wide range of densities.
A difflculty with many prior art aerated or so called "foamed" explosive
combinations resides in obtaining a uniform distribution of small bubbles throughout
the liquid combination and many foamed explosives have a very short shelf-life. A
further difflculty with many prior art foamed explosive combinations is that they are
sensitive and poor travellers. These difficulties have led to the need for foaming the
15 liquid combinations as close to the site of use as is possible.
U.S. Patent Specification No. 3582411 discloses a method for making
a foamed liquid explosives combination by the steps of adding a foam promoting and
viscosity increasing agent, such as a salt water foamer, to a liquid solution, such as
an explosive slurry, blending at least part of the liquid solution with a gas to produce
20 fine bubbles therein, and thereafter mixing the gas-containing liquid with particulate
fuel solids which impart sensitivity to the composition. It should be noted that in this
disclosure the bubbles are not formed within the liquid composition but are introduced
by mechanical means, for example by the apparatus described in the publication. Such
mechanical introduction of gas into the liquid combination, as is well known, does not
25 introduce bubbles of uniform siæ in the density required throughout the liquid
combination, the foamed product has a poor shelf life and the disclosure requires the
addition of fuel solids after the foaming of the liquid, again by a mechanical means,
which can lose gas from the foamed liquid, and, as stated, the addition of the fuel
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solids renders the combination sensitive. Further, the apparatus illustrated is not
suited for location at many sites of use, such as remote quarry sites.
U.S. Patent Specification No. 3586553 proposes the use of proteinaceous
material in a liquid explosives combination and suggests that such material functions
as an effective foaming agent but the specification emphasises mechanical mixing to
introduce gas to the liquid explosives combination and there is no suggestion in this
publication that the proteinaceous material can, without agitation of the liquidexplosives combination, produce gas bubbles within said combination.
U.S. Patent Specification No. 3713919 discloses semi-solid colloidal
dispersions of water-bearing blasting agents including N.N.dinitrosopentamethylene-
tetramine which, it is suggested, is mixed with the explosive mixture at temperatures
between 130F to 180F, whereupon said additive decomposes to form gas bubbles
within the explosive mixture. It should be noted that the size of the bubbles generated
and the distribution of said bubbles through the explosive mixture must be entirely
dependant upon the degree of mixing, mechanical mixing, the mixing operation is
carried out at elevated temperatures and the foamed explosive mixture must be
transported, in foamed condition, to the required location of use.
It is an object of the present invention to obviate or mitigate the above
mentioned disadvantages. Accordingly, the invention provides a foamable explosive
combination comprising a liquid or semi-liquid explosive composition with a low
boiling point liquid dispersed through said composition, said low boiling point liquid
being selected to maintain its liquid form at normal temperature and elevated pressures
and to vaporize at normal temperature and pressure whereby to form gas bubbles
distributed through the said composition.
The explosive combination proposed by the present invention has the
advantages that:
1. it can be held in a very stable condition for long periods and
thereby can have a long, safe, storage life, simply by maintaining the combination
under pressure to hold the low boiling point liquid in liquid form;
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2. said combination can be foamed when required and at the location
of use so that the problems of transporting a foamed sensitive explosive combination
are avoided;
3. the use of a liquid to generate the bubbles avoids the need to
5 mechanically agitate the composition to beat bubbles into the combination;
4. the use of a liquid, dispersed through the explosive composition,
to generate the bubbles allows a more uniform distribution of bubbles than can be
obtained with prior art combinations;
5. the use of a low boiling point liquid to generate the bubbles ;n the
10 composition by vapourization allows the explosive combination to be returned to a
safe, unfoamed, condition simply by pressurizing the foam to reduce the vapouriæd
liquid to liquid form, an important advantage not possible with prior art combinations
which rely on decomposition of an ingredient to generate the gas bubbles.
Preferably said explosive composition comprises the liquid phase of a
15 solution or colloid and the said low boiling point liquid is at least partially contained
within the discontinuous phase of the system.
Preferably the said explosive composition comprises an oxidizing salt-
saturated aqueous solution.
Conveniently the combination may include additional explosive material
20 or materials, in divided form, dispersed through the said explosive composition.
The combination proposed by the invention may conveniently include any
of the liquid, or semi-liquid, explosives compositions known in the art but preferably
comprises a solution or colloid wherein the liquid phase is an oxidizing salt or salts-
saturated aqueous solution. The discontinuous phase then conveniently includes a25 surfactant and the low boiling point liquid whereupon, when exposed to normaltemperature and pressure, the low boiling point liquid forms gas bubbles dispersed
through the discontinuous phase, and thereby through the said continuous phase.
In one embodiment proposed by the invention the foamable explosive
combination is packaged in a container and part of the low boiling point liquid is
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allowed to vapouriæ to pressurize the container contents, thereby to maintain the other
part of said liquid in liquid form.
In another embodiment proposed by the invention the foamable explosive
combination is packaged in a container and all the low boiling point liquid in the
5 combination is maintained in liquid form by pressurizing the combination with a
propellant gas which can maintain the container under pressure during storage
conditions and assist in expelling the explosive combination from the container when
required.
The surfactants involved may be nonionic, cationic or amphoteric in
10 nature or combinations thereof. It (or they) should be capable of producing a suitable
stable oil/water emulsion or dispersion of the selected low boiling point liquid in the
liquid explosive composition. Suitable emulsifiers are amine oxides in combination
with alkanolamides exemplified by stearic monoethanol-amide or tallow mono (di)
ethanolamide. Further emulsifiers which may be used with selected low boiling point
15 liquids are alkyl ethers, alkyl esters and other common types of surfactants.To achieve a satisfactory foam stability the preferred surfactants will be
required to have limited solubility in the oxidiser phase in order that, on ejection from
the container followed by vapourization of the low boiling point liquid, crystallization
or precipitation occurs due to the loss in solvency and/or cooling effect. N.B. In the
20 concentrate the surfactant may be present as a colloidal or other fine dispersion or
dissolved foam at normal temperatures.
In this composition the surface active agent and other organic additives
(see below) may also function as fuel for the explosive combination.
In addition to the surface active materials described above, other non-
25 surface active materials, or low HLB surfactants of low stability may be dispersed oremulsified into the system to further increase foam stability. Such materials,
precipitating/crystallizing or vapourization of the low boiling point liquid add further
strength to the bubble wall. Such materials are exemplified by lauryl, myristyl, catyl,
stearyl and behenyl alcohols, dobanols and similar synthetic mixtures. Other
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additives, potentially useful in this role, would be other wax-like materials such as
natural waxes, synthetic waxes, hydrocarbon waxes, stearyl stearate, myristyl stearate,
glycerol esters, mono, di and triesters of pentaerythritol, trimethylol propane, sorbitol
or other polyol (some of which will also be surface active) of sufficient molecular
S weight to render it crystalline.
Polymers compatible with the system will also function as foam
stabilizers.
The preferred oxidizing salt in the combination is ammonium nitrate.
However, other salts such as X Y Z are equally applicable used alone or in
10 combination with ammonium nitrate.
The oxidizer is preferably included in the combination in the form of a
saturated aqueous solution containing between X and Y% mt/mt oxidiær salt.
The low boiling point liquid is preferably of the so called aerosol type.
Virtually any aerosol propellant compatible with the selected surfactant may be used.
15 Preferably said liquids involve CC12F or CCIF2CCIF2 or combinations thereof or
other halogenated hydrocarbons capable of producing an internal pressure of X - Y
butane, isobutane, propane, pentone, heptane and other low boiling point hydrocarbons
are also suitable, depending upon their compatibility with the selected surfactant(s).
Foam stability is affected by the type of low boiling point liquid selected
20 for the composition and the properties of the low boiling point liquid in the combination will determine the density of the combination when foamed.
When the foamable combination is pressurized in a container by a second
low boiling point liquid said liquid may be selected from the above defined low boiling
point liquids but preferably said second low boiling point liquid is selected to25 vapourize at lower temperature than the low boiling point liquid in the combination
to maintain said liquid in liquid form in the combination.
When the combination is released to normal temperature and pressure
(atmospheric temperature and pressure at the location of use) the low boiling point
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liquid dispersed through the combination vapouriæs very rapidly to foam the
combination.
It is probable that a stable foam results from the bubbles of low boiling
point liquid being surrounded by a liquid saturated solution of oxidizer salt containing
S solid particles of surfactant and/or other matter as described previously, coalescence
of the bubbles being prevented or retarded by the solid particles within the bubble
wall. Foams of extreme stability will result if the oxidiær or oxidizing salt is thrown
out of solution by extreme cooling due to rapid vapourization of the low boiling point
liquid. Hence the foam is formed by vaporization of the dispersed low boiling point
liquid within the oxidizing salt phase, the stability of the foam resulting from the
formation of a solid or solid/liquid wall of aqueous oxidizer salt and particulate
surfactant and/or additive and/or oxidizer salt enabling bubble formation to occur.
When the composition is packaged in a container having means for
controllably releasing the combination the said combination may be released directly
at the location of use with no preparation other than a minor manual shaking to ensure
dispersal of the low boiling point liquid through the combination.
The container may be fully charged with the combination and the low
boiling point liquid to maintain the container under pressure and to propel the
combination from the container at the location or site of use.
When so processed the container preferably has a capacity of at least
20 ml.
In an alternative arrangement the composition, without the low boiling
point liquid or the liquid for pressurizing the container, may be packaged remote from
the location of use and the said liquids added at the location of use.
The means for controllably releasing the composition from a container
may conveniently comprise a manually operable valve mounted on the container or a
nozzle connected to the container by rigid or flexible duct means. Thus the container
may discharge foamable explosive composition in similar manner to a spray can, or
via a wand or boom.
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In one preferred embodiment a cylindrical container with an aerosol type
valve has a discharge tube to the valve extending into the container. A flexible bag
containing the foamable explosive composition has its mouth secured to said discharge
tube so that only the bag contents can be discharged from the valve. A low boiling
S point liquid, selected to vaporiæ at a lower temperature than the low boiling point
liquid in the combination in the bag, is charged into the container externally of the
bag.
With this arrangement the low boiling point liquid externally of the bag
is at least partially vaporiæd at all times to maintain the bag under pressure whereby
to maintain the low boiling point liquid in the composition in liquid form. When the
valve is manually activated explosive composition in the bag is propelled up thedischarge tube and through the valve to atmosphere by the pressure of the vaporiæd
liquid surrounding the bag. On release to atmosphere the low boiling point liquid
dispersed through the explosive combination vaporiæs to form small bubbles within
the explosive combination, thus "foaming" said released combination. This type of
construction allows the combination to be completely discharged from the container
under pressure without any loss of low boiling point liquid from the combination.
The following Examples, in which all percentages are weight, are given
by way of illustration.
An explosive aqueous solution (having all components dissolved at the
ambient temperature 20C) was prepared containing:
47% monmethylamine nitrate
13% water
30% ammonium nitrate, and
10% sodium perchlorate
As emulsifier there was added from 9 to 10% (based on the total weight
of the composition) of an emulsifier consisting of:
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55% Fenopon~ CD 128 (Ammonium salt of ethyloxylated coconut fatty
acid sulphate)
22~ stearic mono-ethanolamide
11% propylene glycol, and
11% cetostearyl alcohol
This emulsifier was warmed until melted and mixed in the aqueous
solution with gentle agitation.
EXAMPLE l
100 g of the composition described above was charged into a
conventional aerosol type container with Sg of Arcton~ 114 (I.C.I.), a commercially
available aerosol propellant. When the container was discharged, under pressure
generated by vaporization of the Arcton 114, the discharge combination foamed,
clearly illustrating that part of the Arcton 114 had been absorbed into the combination
and vaporiæd on discharge.
EXAMPLE 2
100 g of the composition described above was charged into a
conventional aerosol type container with 5g of CC12 F2 (Propellant 12). When thecontainer was discharged the discharging combination foamed, again clearly
illustrating that part of the propellant had been absorbed in liquid form into the
combination and vaporized within the combination on exposure to atmosphere.
It will be appreciated that in both the above examples the low boiling
point liquid serving to foam the combination served the dual purpose of expelling the
composition from the container and whilst both the above embodiments fulfilled all the
requirements of the invention there is difficulty with such dual purpose low boiling
point liquids in controlling the volume of gas within the foam whilst maintaining a
uniform pressure for the discharge.
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EXAMPLE 3
100 g of the composition described above was charged into a flexible bag
with lg of CCIF2 CCIF2 (Propellant 114) and the mouth of the bag was secured to the
discharge tube of a conventional aerosol type valve in an aerosol container. A volume
5 of 5g of propellant 114 was charged into the container to surround the bag.
On discharge of this arrangement it was found that virtually all the
propellant 114 within the bag formed small gas bubbles distributed through the
discharge composition and the propellant surrounding the bag discharged the bag
contents at substantially uniform pressure. As the propellant within the bag,
10 constituting the low boiling point liquid within the explosive combination, was all
expelled within the explosive combination it will be readily seen that the proportion
of the low boiling point liquid in the explosive combination can be varied to give
desired foam densities to the foamed combinations, and combinations with the gasphase between 10% and 90% of the volume of the foamed combination can be readily15 and easily obtained.
As is known, finely divided metal powder such as aluminum powder, or
finely divided self explosive material such as PETN may be suspended in the
combination to further increase its explosive power.
