Explosive compositions based on time-stable colloidal dispersions

A water-in-oil explosive composition based on colloidal dispersions is provided. Unlike conventional emulsion explosive compositions, the microemulsion composition of the invention displays exceptional long term storage stability retaining sensitivity to propagation even in small diameter charges. The composition is also tolerant to doping with further fuel and energy enhancing ingredients. The microemulsion-producing component of the composition comprises a combination of at least one conventional water-in-oil emulsifier and at least one amphiphatic synthetic polymeric emulsifier selected from graft, block or branch polymers.

This invention relates to waterproof explosive compositions based on 
ultra-stable colloidal dispersions. More particularly, this invention 
relates to explosive compositions comprising, in part or in whole, a 
water-in-oil microemulsion which results from the use of blends of 
specific emulsifiers and co-surfactants. 
Conventional low cost commercial explosives rely on ammonium nitrate as the 
primary source of energy for blasting. Ammonium nitrate/fuel oil 
compositions (ANFO) and thickened water-based ammonium nitrate-containing 
explosives (slurries) are widely used blasting compositions. However, 
these compositions may not produce optimum results under conditions 
frequently encountered in the field nor are these compositions always 
acceptable from other standpoints. The use of ANFO, for example, is 
generally restricted to fairly dry boreholes. Also, ANFO does not perform 
well in blasting hard rock because of its low brisance and low bulk 
energy. The development of the pumpable water-based slurries has overcome 
some of the problems, but the need to incorporate special thickening and 
cross-linking agents in the slurries increase their cost. Also, for these 
slurry compositions to perform well, especially in small diameter charges, 
their density and hence their bulk energy must be appreciably lowered if 
the incorporation of large amounts of self-explosive sensitizing agents is 
to be avoided. 
The discovery of water-in-oil emulsion explosives in which the oil/fuel 
phase is external or continuous and the oxidizer salt phase comprising 
dispersed small supersaturated droplets is discontinuous, has resulted in 
a pumpable, fluid explosive which in many instances displays improved 
performance over the water-based slurries. This improvement results 
principally because the surface area of contact between the oxidizer phase 
and the fuel phase is increased. This enhanced intimacy produces a more 
sensitive and faster reacting mixture and provides a high brisance 
explosive. 
Water-in-oil emulsion explosives are now well known in the explosives art. 
Bluhm, in U.S. Pat. No. 3,447,978 discloses a composition comprising an 
aqueous discontinuous phase containing dissolved oxygen-supplying salts, a 
carbonaceuous fuel continuous phase, an occluded gas and a water-in-oil 
emulsifier. Cattermole et al., in U.S. Pat. No. 3,674,578 describe a 
similar composition containing as part of the inorganic oxidizer phase, a 
nitrogen-base salt such as an amine nitrate. Tomic, in U.S. Pat. No. 
3,770,522 also describes a similar composition wherein the emulsifier is 
an alkali or ammonium stearate. Wade, in U.S. Pat. No. 3,715,247 describes 
a small-diameter cap-sensitive emulsion type explosive composition 
comprising carbonaceous fuel, water, inorganic salts, an emulsifier, gas 
bubbles, and a detonation catalyst consisting of a water-soluble salt 
containing selected metals. In U.S. Pat. No. 3,765,964, Wade describes an 
improvement in the composition of U.S. Pat. No. 3,715,247 by including 
therein a water-soluble strontium compound to provide further sensitivity. 
Wade again, in U.S. Pat. No. 4,110,134 describes an emulsion type 
explosive composition devoid of any self explosive ingredient and 
containing a closed-cell void-containing material as a density controller. 
Wade further describes, in U.S. Pat. No. 4,149,916, a cap sensitive 
emulsion type explosive composition containing perchlorates and occluded 
air and in U.S. Pat. No. 4,149,917 he describes a similar composition 
without any sensitizer other than occluded air. Sudweeks and Jessop in 
U.S. Pat. No. 4,141,767 describe a cap-insensitive water-in-oil emulsion 
explosive composition containing a fatty acid amine or ammonium salt 
emulsifier having a chain length ranging from 14 to 22 carbon atoms. In 
applicant's copending Canadian application Ser. No. 317,649, filed on Dec. 
8, 1978, there is described a sensitive emulsion type explosive 
composition containing fuel, water, salts, gas bubbles, an emulsifier and 
an emulsification promoter comprising a highly chlorinated paraffinic 
hydrocarbon. Clay, in U.S. Pat. No. 4,111,727 describes a blasting 
composition consisting of a greasy, water-in-oil emulsion admixed with a 
substantially undissolved particulate solid oxidizer salt constituent so 
as to fill the interstices between salt particles to increase the bulk 
density of the mass. Similar blasting compositions had also been disclosed 
by Egly and Neckar in U.S. Pat. No. 3,161,551 and by Butterworth in South 
African patent specification No. 71/3355. Mullay, in U.S. Pat. No. 
4,104,092 describes an aqueous gel explosive composition wherein a 
water-in-oil emulsion is uniformly distributed in the gel portion. 
While all of the aforementioned emulsion compositions are meritorious, they 
are not without some disadvantages. The composition of Bluhm, for example, 
is only suitable for use in large diameter charges and requires strong 
primer initiation. The compositions of Cattermole et al. while useful in 
small diameter charges, require the use of expensive raw materials, demand 
extra handling precautions because of the sensitive nature of some of the 
ingredients used and hence lead to increase costs. 
The compositions of Wade, and other prior art water-in-oil emulsion-based 
explosives exhibit limited stability. These compositions quickly tend to 
become dry and hard upon aging which condition deleteriously affects their 
handling characteristics and their explosive performance. The emulsifying 
agents used heretofore have not been sufficiently effective in permanently 
suppressing the coalescence of the supersaturated oxidizer salt droplets. 
Fairly large quantities of perchlorate salts or other sensitizing agents 
must be incorporated in the mixtures in order to retain cap-sensitivity at 
densities above 1.10 g/cc for any appreciable period of time. The 
compositions of Clay are substantially similar to and behave like ANFO and 
can not be expected to offer much improved water resistance. Furthermore, 
any of the composition containing added excess salts would exhibit very 
limited stability because of the seeding or precipitation effect of the 
salt crystals leading to a fairly rapid breakdown of the emulsion. 
Thus, there remains a need in the explosives art for a low cost, high 
velocity and relatively high density explosive which is easy to 
manufacture, pumpable, water resistant and more importantly, which is safe 
to handle, stable over long periods of storage and sufficiently sensitive 
to propagate in very small diameter boreholes. The present invention 
provides an improved water-in-oil emulsion explosive composition which 
meets all the above-mentioned objectives. 
The effectiveness of emulsification of the aqueous salts and liquid fuels 
as a promoter of explosive performance is crucially dependent on the 
activity of the emulsifying agent chosen. The emulsifying agent aids the 
process of droplets subdivision and dispersion in the continuous phase by 
reducing the surface tension and the energy required to create new 
surfaces. The emulsification agent also reduces the rate of coalescence by 
coating the surface of the droplets with a molecular layer of the 
emulsifying agent. The emulsifiers employed in the aforementioned prior 
art explosive compositions are somewhat effective in performing these 
functions but they are limited in their utility because the droplet 
surfaces still contain energy and coalescence of the droplets and 
breakdown of the emulsion takes place over time. 
The emulsifier systems of the present invention are of a novel and distinct 
class of materials which function to produce a water-in-oil microemulsion. 
In the context of the present invention, the term 'microemulsion is 
intended to denote a liqui-liquid foam of very small cell size ranging 
normally from less than 1 micron to about 15 microns. These microemulsions 
demonstrate a surprising stability and retention of initiation 
sensitivity, and they possess extreme intimacy of mixing which is 
achievable under a variety of mixing conditions. The novel emulsifier 
systems of this invention provide means whereby water-in-oil 
microemulsions may be formed with concentrated oxidizer salt(s) common in 
explosive formulations. 
The water-in-oil microemulsion explosive compositions of the invention 
comprise essentially an aqueous solution of at least one oxygen-supplying 
salt as a discontinuous phase, an insoluble liquid or liquefiable 
carbonaceous fuel as a continuous phase, at least one sensitizing 
component distributed substantially homogeneously throughout the 
composition as a further discontinuous phase and a distinct definable 
blend of emulsifying agents capable of producing a time-stable 
microemulsion. The compositions may optionally contain particulate 
oxygen-supplying salts, ANFO, particulate light metals, particulate fuels, 
particulate solid explosives, soluble and partly soluble self-explosives, 
explosive oils and the like for purposes of augmenting the strength and 
sensitivity or decreasing the cost of the compositions. The specific 
blends of emulsifiers capable of producing a time-stable, water-in-oil 
microemulsion explosive composition comprise a mixture of at least one 
amphiphatic synthetic polymeric emulsifier selected from graft, block or 
branch polymers and at least one conventional water-in-oil emulsifier. 
Optionally a phosphatide emulsion stabilizer may be included in the blend. 
By "amphiphatic graft, block or branch polymers" is meant a polymer 
comprising at least two or more segments, one of which is only soluble in 
an oil phase and the other only soluble in an aqueous phase, each segment 
having a molecular weight of at least 500. By "conventional water-in-oil 
emulsifier" is meant herein the relatively low molecular weight 
emulsifiers which are capable of producing a water-in-oil emulsion. Most 
of these emulsifiers are listed in the well known publication 
"McCutcheon's Detergents & Emulsifiers". 
Exemplary of the synthetic polymeric emulsifiers used in the combinations 
are: 
A. Copolymers of the general formula (A-COO).sub.m -B wherein m is 2, 
wherein each polymeric component A has a molecular weight of at least 500 
and is the residue of an oil-soluble complex monocarboxylic acid having 
the general structural formula: 
##STR1## 
in which R is hydrogen or a monovalent hydrocabon or substituted 
hydrocarbon group; 
R.sub.1 is hydrogen or a monovalent C.sub.1 to C.sub.24 hydrocarbon group; 
R.sub.2 is a divalent C.sub.1 to C.sub.24 hydrocarbon group; 
n is zero or 1; 
p is an integer from zero up to 200; 
and wherein each polymeric component B has a molecular weight of at least 
500 and is the divalent residue of a water-soluble polyalkylene glycol 
having the general formula: 
##STR2## 
in which R.sub.3 is hydrogen or C.sub.1 to C.sub.3 alkyl group; 
q is an integer from 10 up to 500. 
The units of the formula 
##STR3## 
which are present in the molecule of the complex monocarboxylic acid as 
represented by Formula I may all be the same or they may be different in 
respect of R.sub.1, R.sub.2 and n. Similarly, the units of the formula 
##STR4## 
which are present in the polyalkylene glycol as represented by Formula II 
may all be the same or they may be different in respect of R.sub.3. 
The complex monocarboxylic acid, from which the polymeric components A are 
derived by the notional removal of the carboxyl group, is structurally the 
product of interesterification of one or more monohydroxy-monocarboxylic 
acids together with a monocarboxylic acid free from hydroxyl groups which 
acts as a chain terminator. The hydrocarbon chains R, R.sub.1 and R.sub.2 
may be linear or branched. R is preferably an alkyl group containing up to 
25 carbon atoms, for example a straight-chain C.sub.17 H.sub.35 -group 
derived from stearic acid. R.sub.1 is preferably a straight-chain alkyl 
group, and R.sub.2 is preferably a straight-chain alkylene group; for 
example, the unit containing R.sub.1 and R.sub.2 may be derived from 
12-hydroxystearic acid. 
The polyalkylene glycol of the Formula II, from which the polymeric 
component B is derived by the notional removal of the two terminal 
hydroxyl groups, may be, for example, a polyethylene glycol, a 
polypropylene glycol, a mixed poly (ethylene-propylene) glycol or a mixed 
poly(ethylene-butylene) glycol, but preferably a polyethylene glycol. 
Preferably each of the polymeric components A has a molecular weight of at 
least 1000 (by "molecular weight" is meant number average molecular 
weight). Thus where, for example, the group R is derived from stearic acid 
and the unit containing R.sub.1 and R.sub.2 together is derived from 
12-hydroxystearic, p will have a value of at least 2. Similarly, it is 
preferred that the polymeric component B has a molecular weight of at 
least 1000. Thus where that component is the residue of a polyalkylene 
glycol which is derived from ethylene oxide exclusively, q will preferably 
have a value of at least 23. 
For optimum results for purposes of the present invention the proportion of 
polymeric component B in the copolymer is between about 20% to 50%, 
preferably 25% to 35% by weight of the total copolymer. 
B. Polyesters obtained by the condensation of 
(i) an alk(en)yl succinic anhydride of the formula 
##STR5## 
where R is a saturated or unsaturated hydrocarbon substituent derived 
from a polymer of a mono-olefin, the said polymer comprising a chain 
containing from 40-500 carbon atoms, and 
(ii) a polyalkylene glycol which has a molecular weight of 500 to 20,000. 
The polyester so obtained contains 10% to 80%, preferably 20% to 60%, by 
weight of residues of the polyalkylene glycol (ii). 
The alk(en)yl succinic anhydrides which are used in making the polyester 
are known commercial materials. For making the anhydrides (i), suitable 
polyolefins include those obtained by polymerising a mono-olefin 
containing from 2 to 6 carbon atoms, for example ethylene, propylene, 
butylene, isobutylene and mixtures thereof, the derived polymers 
containing from 40 to 500 carbon atoms in the chain as stated heretofore. 
A preferred alk(en)yl succinic anhydride is (polyisobutenyl) succinic 
anhydride containing from 50 to 200 carbon atoms in the alkenyl chain. 
The alk(en)yl succinic anhydrides (i) may, however, if desired be a mixture 
of two or more different compounds which respectively satisfy the 
foregoing definitions. A minor proportion of a monobasic carboxylic acid 
may be included to adjust the functionality and/or degree of branching of 
the derived polyesters. 
The polyalkylene glycols (ii) which are used in making the polyesters may 
be, for example, polyethylene glycols, mixed poly(ethylene-propylene) 
glycols or mixed poly(ethylene-butylene) glycols, provided that they 
satisfy the molecular weight requirement hereinbefore stated. The 
polyalkylene glycols are also commercially available materials, and a 
single such compound or a mixture of two or more such compounds differing 
in composition and/or molecular weight may be used in making the 
polyesters if desired. 
Preferred polyalkylene glycols for use in making the polyesters are 
polyethylene glycols of average molecular weight 500 to 1,500. 
In addition to the polyalkylene glycol(s), other polyols such as glycerol, 
trimethylol propane, pentaerythritol and sorbitol may be incorporated in 
order to adjust the overall functionality of the components and/or 
increase the degree of branching of the polymers. 
C. Alkyd resins obtained by the condensation of a polybasic acid or 
anhydride, usually in combination with a monobasic acid, and a polyhydric 
alcohol. 
The polybasic acid component of the alkyd resin may be saturated, or 
unsaturated either by olefinic or aromatic unsaturation. Commonly used 
acids are aliphatic or aromatic dibasic acids containing up to 20 carbon 
atoms, preferably up to 10 carbon atoms such as, for example, ortho-, iso- 
or terephthalic acid, maleic acid and fumaric acid. The polybasic acid may 
also be tri- or tetra-basic, suitably an aromatic acid containing up to 
20, preferably up to 10 atoms such as, for example, trimellitic acid or 
pyromellitic acid. 
The optional monobasic acid component of the alkyd resin, which functions 
as a monofunctional chain terminator, may be derived from a free acid or 
from an ester of the acid, particularly a glyceride. The acid is 
preferably an aliphatic saturated or ethylenically unsaturated acid 
containing up to 30 carbon atoms, preferably 6 to 22 carbon atoms. 
Mixtures of acids or their esters may also be used to derive the 
mono-basic acid component, particularly naturally-occurring mixtures such 
as tall oil acids, or acids derived from linseed oil, soybean oil, castor 
oil, cottonseed oil and the like. Other monobasic acid chain terminators 
known to those expert in the field may also be used as may monohydric 
alcohol chain terminators which are also known for this purpose, for 
example, C.sub.1 to C.sub.20 alkanols. 
The polyhydric alcohol is a water-soluble polyalkylene glycol which has a 
molecular weight in the range of 500 to 10,000 preferably 500 to 5,000. 
The water-soluble polyalkylene glycol is preferably polyethylene glycol, 
but polypropylene glycol or polyalkylene glycols containing a major 
proportion of ethyleneoxy groups together with minor proportions of 
randomly distributed propyleneoxy and/or butyleneoxy groups may also be 
used. One of the terminal hydroxyl groups of the polyalkylene glycol may, 
if desired, be etherified, for example, with a lower C.sub.1 to C.sub.6 
alcohol. 
D. Copolymers as described in A but with the polyoxyethylene chain of the 
polyalkylene glycol moiety replaced by a polyethylene-imine chain (i.e. 
replacing the oxygen atom in the polyoxyethylene by a N-H group). 
The substitution of the polyoxyethylene chain of the polyalkylene glycol of 
the block copolymers A by a polyethyleneimine chain does not significantly 
alter the emulsifying ability of these resins. The proportion of polymeric 
components in the block copolymer of these polyethylene-imine based 
polymers are as described in the types A. Also these polymers can be 
largely a salt or an amide depending on the conditions present during 
their synthesis. 
Exemplary of the conventional water-in-oil emulsifiers with which the 
amphiphatic polymeric emulsifiers of the above-described types A, B, C and 
D are combined in order to produce the microemulsion explosive 
compositions of this invention are: 
E. Those derived from sorbitol by esterification such as sorbitan fatty 
acid esters, for example, sorbitan monooleate, sorbitan sesquioleate, 
sorbitan monostearate and the like; 
F. Mono and diglycerides of fat-forming fatty acids such as Atmos 300 (Reg. 
TM), Dur-Em 187 (Reg. TM), Dur-Em 207 (Reg. TM) and the like; 
G. Polyoxyethylene sorbitol esters such as polyoxyethylene sorbitol beeswax 
derivative materials and the like; 
H. Substituted imidazolines such as Witcamine PA-78B (Reg. TM) and the 
like; 
I. Aliphatic amido-amines such as Witcamine 210 (Reg. TM) and the like; 
J. Glycerol esters such as glycerol monooleate, glycerol monostearate, 
decaglycerol decaoleate and the like; 
K. Fatty acid amines or ammonium salts such as Armac HT (Reg. TM) and the 
like; 
L. Hydrocarbon sulphonate salts such as the petroleum sulphonates and more 
particularly sodium petroleum sulphonates and the like; and 
M. Alkali metal or ammonium stearates used alone or in combination with 
stearic acid. 
It has been found that an optional phosphatide emulsion stabilizer in 
admixture with the polymeric emulsifier(s) and the conventional 
water-in-oil emulsifier(s) can be employed to yet further improve the long 
term stability and sensitivity of the emulsion. Particularly effective 
phosphatides are those having the structural formula 
##STR6## 
wherein M is selected from the class consisting of fatty acyl radicals and 
phosphorus-containing radicals having the structural grouping 
##STR7## 
wherein R' is a lower alkylene radical having from 1 to about 10 carbon 
atoms and R", R'" and R"" are lower alkyl radicals having from 1 to 4 
carbon atoms and wherein at least one but no more than one of the M 
radicals comprise the phosphorus-containing radical. The fatty acyl 
radicals are for the most part those derived from fatty acids having from 
8 to 30 carbon atoms in the fatty radicals such as, for example, palmitic 
acid, stearic acid, palmitoleic acid, oleic acid and linoleic acid. 
Especially desirable radicals are those derived from commercial fatty 
compounds such as soybean oil, cotton seed oil, castor seed oil and the 
like. A particularly effective phosphatide is soybean lecithin. 
The ratio of polymeric emulsifier(s) to conventional water-in-oil 
emulsifier(s) is in the range of 1:25 to 3:1, but preferably in the range 
of 1:5 to 1:1. The total quantity of the mixed emulsifiers found suitable 
for use is from 0.4% to 4%, preferably from 0.6% to 1.6% by weight of the 
total microemulsion composition. The quantity of optional phosphatide 
stabilizer which can be used is from 0.05% to 5.0%, preferably from 0.5% 
to 1.5% of the total microemulsion composition. The ratio of mixed 
emulsifiers (polymeric plus conventional) to the phosphatide stabilizer 
can be in the range of 1:10 to 100:1 but preferably is in the range of 1:3 
to 5:1. 
The preferred inorganic oxygen-supplying salt suitable for use in the 
water-in-oil microemulsion composition is ammonium nitrate; however a 
portion of the ammonium nitrate may be replaced by other oxygen-supplying 
salts such as alkali or alkaline earth metal nitrates, chlorates, 
perchlorates or mixtures thereof. The quantity of oxygen-supplying salt 
used in the water-in-oil microemulsion may range from 30% to 90% by weight 
of the total composition. 
Suitable water-immiscible emulsifiable fuels for use in the water-in-oil 
microemulsion include most hydrocarbons, for example, paraffinic, 
olefinic, naphthenic, elastomeric, aromatic, saturated or unsaturated 
hydrocarbons. Preferred among the water-immiscible emulsifiable fuels are 
the highly refined paraffinic hydrocarbons. The quantity of liquid or 
liquefiable carbonaceous fuel used in the water-in-oil microemulsion may 
comprise up to 20% by weight of the total composition. 
The sensitizing component distributed substantially homogeneously 
throughout the composition is preferably occluded gas bubbles which may be 
introduced in the form of glass or resin microspheres or other 
gas-containing particulate materials. Alternatively, gas bubbles may be 
generated in-situ by adding to the composition and distributing therein a 
gas-generating material such as, for example, an aqueous solution of 
sodium nitrite. Other suitable sensitizing components which may be 
employed alone or in addition to the occluded or in-situ generated gas 
bubbles include insoluble particulate solid self-explosives such as, for 
example, grained or flaked TNT, DNT, RDX and the like and water soluble 
and/or hydrocarbon soluble organic sensitizers such as, for example, amine 
nitrates, alkanolamine nitrates, hydroxyalkyl nitrates, and the like. The 
explosive compositions of the present invention may be formulated for a 
wide range of applications. Any combination of sensitizing components may 
be selected in order to provide an explosive composition of virtually any 
desired density, weight-strength or critical diameter. 
The quantity of solid self-explosive ingredients and of water-soluble 
and/or hydrocarbon-soluble organic sensitizers may comprise up to 40% by 
weight of the total composition. The volume of the occluded gas component 
may comprise up to 50% of the volume of the total explosive composition. 
Optional additional materials may be incorporated in the composition of the 
invention in order to further improve sensitivity, density, strength, 
rheology and cost of the final explosive. Typical of materials found 
useful as optional additives include, for example, emulsion promotion 
agents such as highly chlorinated paraffinic hydrocarbons, particulate 
oxygen-supplying salts such as prilled ammonium nitrate, calcium nitrate, 
perchlorates, and the like, ammonium nitrate/fuel oil mixtures (ANFO), 
particulate metal fuels such as aluminium, silicon and the like, 
particulate non-metal fuels such as sulphur, gilsonite and the like, 
particulate inert materials such as sodium chloride, barium sulphate and 
the like, water phase or hydrocarbon phase thickeners such as guar gum, 
polyacrylamide, carboxymethyl or ethyl cellulose, biopolymers, starches, 
elastomeric materials, and the like, crosslinkers for the thickeners such 
as potassium pyroantimonate and the like, buffers or pH controllers such 
as sodium borate, zinc nitrate and the like, crystals habit modifiers such 
as alkyl naphthalene sodium sulphonate and the like, liquid phase 
extenders such as formamide, ethylene glycol and the like and bulking 
agents and additives of common use in the explosives art. 
The quantities of optional additional materials used may comprise up to 50% 
by weight of the total explosive composition, the actual quantities 
employed depending upon their nature and function. 
The preferred methods for making the water-in-oil microemulsion explosive 
compositions of the invention comprise the steps of (a) mixing the water, 
inorganic oxidizer salts and, in certain cases, some of the optional 
water-soluble compounds, in a first premix, (b) mixing the carbonaceous 
fuel, emulsifying agent and any other optional oil soluble compounds, in a 
second premix and (c) adding the first premix to the second premix in a 
suitable mixing apparatus, to form a water-in-oil microemulsion. The first 
premix is heated until all the salts are completely dissolved and the 
solution may be filtered if needed in order to remove any insoluble 
residue. The second premix is also heated to liquefy the ingredients. Any 
type of apparatus capable of either low or high shear mixing can be used 
to prepare the microemulsion explosives of the invention. Glass 
microspheres, solid self-explosive ingredients such as particulate TNT, 
solid fuels such as aluminium or sulphur, inert materials such as barytes 
or sodium chloride, undissolved solid oxidizer salts and other optional 
materials, if employed, are added to the microemulsion and simply blended 
until homogeneously dispersed throughout the composition. 
The water-in-oil microemulsion of the invention can also be prepared by 
adding the second premix liquefied fuel solution phase to the first premix 
hot aqueous solution phase with sufficient stirring to invert the phases. 
However, this method usually requires substantially more energy to obtain 
the desired dispersion than does the preferred reverse procedure. 
Alternatively, the water-in-oil microemulsion is particularly adaptable to 
preparation by a continuous mixing process where the two separately 
prepared liquid phases are pumped through a mixing device wherein they are 
combined and emulsified. 
Characteristic of the novel explosive compositions of the invention is the 
unique nature of the water-in-oil microemulsion which results from the use 
of specific blends of emulsifiers. The microemulsion of the invention is a 
demonstrably different state of matter than any of previously disclosed, 
conventional prior art explosive emulsions. Several techniques well known 
to those experienced in the art, may be employed to differentiate the 
microemulsions of this invention from the conventional explosive emulsions 
of the prior art. 
Microcalorimetry 
The novel emulsifiers employed in the composition of this invention differ 
from prior art systems in that a highly ordered and stable film is 
produced. This stability is a consequence of the energy release on 
formation of the film which energy release exceeds the newly created 
surface energy. The microemulsions created therefore, have an energy 
barrier towards coalescence which barrier does not exist with prior art 
emulsifiers. Microcalorimetry may be used to observe the free energy 
change of mixing. A typical microemulsion of the present invention had a 
highly negative free energy change of mixing (-5 to -7 .sup.J /g of oil 
phase), on the other hand, a representative prior art emulsion formed from 
sorbitan sesqui-oleate had a much smaller free energy change of mixing 
closely approaching zero (-0.5 to -0.9 J/g of oil phase). This substantial 
energy difference helps explain the stability of the microemulsions of the 
present invention. 
Ease of Mixing 
As further evidence for ease of formation and for intrinsic stability, a 
microemulsion was prepared by simply pouring an aqueous oxidizer salt 
solution into an hydrocarbon fuel solution containing the emulsifying 
system of the present invention while stirring by hand with a slow spatula 
action. This extremely low shear mixing was sufficient to produce a stable 
water-in-oil microemulsion explosive composition which was subsequently 
aerated to a density of 1.10 g/cc, packaged in a 25 mm diameter cartridge 
and detonated at 5.degree. C. with an ordinary electric blasting cap. 
After several weeks of storage this composition was still detonator 
sensitive and no visual signs of destabilization were observed. 
X-Ray diffraction 
All prior art explosive emulsions show gradually increasing crystal growth 
and structure upon storage as a consequence of their instability and slow 
coalescence of the aqueous oxidizer salt droplets. This increasing crystal 
structure can be easily detected by X-ray diffraction. The microemulsion 
explosives of this invention show no such X-ray diffraction pattern even 
at very low temperature or after prolonged storage and/or for compositions 
containing extremely low levels of water. 
Sedimentation 
To further differentiate the microemulsion explosives of this invention 
from prior art emulsion explosives, centrifugation experiments were 
conducted to observe sedimentation rates. After 30 minutes of 
ultracentrifugation at 35,000 G's, the microemulsions of the present 
invention devoid of any insoluble optional additives remained virtually 
intact as opposed to substantial crystallization and/or phase separation 
for all prior art emulsion explosives tested. 
The following Examples and Tables demonstrate the unique properties of the 
microemulsion explosive compositions of the invention.