Shaped explosive by recrystallization from a non-aqueous self-explosive emulson

An explosive composition is derived from a non-aqueous emulsion of a solution of a self-explosive dispersed as the discontinuous phase (D-phase) throughout a continuous phase (C-phase) which is substantially immiscible with the D-phase. The emulsion is prepared by dropping the solution of self-explosive into a dispersion of surfactant or emulsifier in fuel, at a temperature high enough to prevent precipitation of the self-explosive from solution. Upon cooling and aging, the emulsion becomes a pourable or pumpable mass which gradually is destabilized. Upon destabilization and recrystallization in a cavity, a mass of crystals of self-explosive becomes shaped to the cavity.

BACKGROUND OF THE INVENTION 
This invention relates to a non-aqueous shaped explosive composition having 
a relatively high density and energy, formed when a hot solution of a 
self-explosive is emulsified with a surfactant-fuel mixture and the 
emulsion destabilizes upon cooling and aging. By "self-explosive" I refer 
to an organic material which can be detonated by itself, for example, with 
a conventional blasting cap. The self-explosive I use is a compound which 
contains at least one nitro- or nitramine group. 
Prior art non-aqueous systems are referred to as melt-in-oil or 
melt-in-fuel emulsions such as disclosed in U.S. Pat. No. 4,248,644 in 
which the fuel or continuous phase contains a surfactant, and the molten 
oxidizer is dispersed throughout the fuel or continuous phase ("C-phase") 
by adequate agitation of the mixture which is then allowed to cool. The 
molten oxidizer is not a self-explosive, that is, it is a 
non-self-explosive (hereafter "oxidizer"). Upon cooling, the result is 
that the oxidizer forms an internal or discontinuous phase ("D-phase") of 
discrete droplets dispersed throughout the continuous (fuel) phase. This 
"stability" permits the droplets to supercool and remain more or less 
fluid or grease-like in texture at a temperature below that at which the 
emulsion was formed. 
In the prior art, with very few exceptions, explosive compositions focus 
the criticality of a stable emulsion which prevents the self-explosive 
from recrystallizing. It was essential that the emulsion be stable and 
that no recrystallization of the non-self-explosive (oxidizer) occurred. 
If recrystallization occurred, the composition would fail to function as 
an explosive. In my invention, it is essential that there be 
recrystallization of the self-explosive after destabilization of the 
emulsion, or the composition would fail to function as a self-explosive. 
For example, U.S. Pat. No. 4,566,919 discloses forming a melt or solution 
of ammonium nitrate in water, at a temperature above the salt 
crystallization temperature. The melt, or first solution, is then added to 
a solution of the emulsifier and an immiscible organic liquid fuel, while 
stirring, to produce a water-in-oil emulsion. The oxidizer is thus 
dispersed in the fuel phase, initially as droplets of solution at elevated 
temperature, and as the composition cools, the precipitation of the salts 
within the droplets is physically inhibited resulting in a stable emulsion 
with enhanced intimacy between oxidizer and fuel. In contrast, because the 
liquids are immiscible organic liquids, no water-in-oil emulsion is formed 
in my composition; the emulsifier is inert; the solvent in the D-phase and 
the liquid fuel in the C-phase are each essentially anhydrous, so that the 
emulsion formed is non-aqueous; and, the self-explosive is dissolved in 
the solvent phase. 
More particularly, the emulsion from which the explosive of my invention is 
derived, is formulated at an elevated temperature, above that at which the 
self-explosive will crystallize from its solution (referred to herein as a 
"nitrosolution"). The emulsion consists essentially of a discontinuous 
nitrosolution phase (D-phase, for brevity) which is dipersed in a 
continuous phase of surfactant and fuel (C-phase, for brevity). The 
solution of self-explosive in organic solvent for the self-explosive is 
referred to herein as a "nitrosolution" because it is a single phase. The 
organic solvent for the nitro-containing or nitramine-containing 
self-explosive is referred to as a "nitrosolvent". 
The surfactant-in-fuel C-phase consists essentially of at least two phases. 
The C-phase is a dispersion of surfactant and fuel. After forming the 
dispersion which is to provide the C-phase, the nitrosolution phase is 
added with vigorous mixing so as to homogeneously distribute the 
nitrosolution as the D-phase in the emulsion so formed. The emulsion is 
formed at a temperature above the recrystallization temperature. By 
"recrystallization temperature" I refer to the temperature at which 
crystals of self-explosive commence to form upon cooling a saturated 
solution of the self-explosive in essentially pure solvent. 
The surfactant may function as the emulsifier, and vice versa. In those 
instances where the surfactant does not function as an emulsifier, an 
emulsifier is also added. It is essential that the surfactant and/or 
emulsifier be unreactive with the nitrosolvent, and therefore each is 
referred to as being substantially inert. Properly formulated, the 
composition is a thick, creamy or waxlike, pourable or pumpable emulsion 
which is poured while hot into a cavity and allowed to crystallize into a 
hard mass upon cooling to ambient temperature. 
Heretofore, shapeable self-explosives (explosives) formed from 
self-explosives such as TNT, pentolite, composition B and the like, were 
prepared by a kettle procedure in which the material was melted and 
continuously mixed to ensure homogeneity, and the melt was then cast. But 
the cast melt shrunk upon cooling, suffered from gradient separation in 
those instance in which the cast melt was a blend (such as in composition 
B), and the skrinkage and separation was such that the characteristics of 
the explosive were generally less predictable than desired. Moreover, 
because of the sensitivity of TNT and other molten self-explosives, the 
process was not particularly safe at the elevated temperatures required 
for preparing the castable melt. The explosive of this invention uses a 
solution of the self-explosive which is substantially insensitive, making 
it safer to handle than prior art compositions. The pourable mixture (from 
which the explosive is derived) can be shaped in a molding cavity without 
significant shrinkage or gradient separation. 
SUMMARY OF THE INVENTION 
It has been discovered that a non-aqueous dispersion of surfactant-in-fuel 
provides the continuous phase (C-phase) for a nitrosolution discontinuous 
phase (D-phase) of an organic self-explosive selected from the group 
consisting of poly(nitroaromatic) solids and nitramine solids, such that 
the C-phase remains the C-phase in an emulsion of 
nitrosolution/surfactant-in-fuel, even when the C-phase is present only as 
a thin film surrounding individual D-phase microdroplets of nitrosolution. 
The peculiar morphology of the composition is realized only when the 
nitrosolution is non-reactive with and immiscible in the fuel. When the 
emulsion is cooled sufficiently below the recrystallization temperature, 
typically to ambient temperature, and aged, the self-explosive 
crystallizes to produce a shaped mass of discrete self-explosive crystals 
conforming to the arbitrary shape and size of a cavity in which the 
emulsion is held. 
It is therefore a general object of this invention to provide an explosive 
composition which comprises a non-aqueous emulsion of a nitrosolution of 
organic self-explosive in a surfactant-in-fuel dispersion, which emulsion 
is formed at an elevated temperature which is above the recrystallization 
temperature of the self-explosive. The emulsion then is supercooled 
allowing it to be manipulated in a fluid or paste-like state and shaped. 
The emulsion having limited stability, upon further cooling and aging, 
inverts, so that the self-explosive subsequently forms a mass of discrete 
crystals. The self-explosive is selected from the group consisting of a 
solid having a nitro- or nitramine- group; said nitrosolution being formed 
with a first liquid with which said self-explosive forms a single phase at 
said elevated temperature; said dispersion being formed with a second 
liquid which provides the fuel, provided said fuel second liquid and said 
solvent first liquid are immiscible, that is, do not form a single phase; 
and, said emulsion is formed with an inert surfactant or emulsifier. 
It is a specific object of this invention to provide a shaped mass of high 
energy explosive comprising discrete crystals of a nitramine such as HMX 
and/or RDX, optionally in combination with a nitroaromatic compound such 
as but not limited to trinitrotoluene, the crystals being in 
crystal-to-crystal contact, and in which mass is trapped separate phases 
of the solvent (first liquid), surfactant or emulsifier, and fuel (second 
liquid), as microdomains, whereby the mass may be detonated. 
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
In general, the self-explosive, or mixture of self-explosives, selected to 
form the hot nitrosolution is chosen by the essential criterion that the 
self-explosive(s) be soluble, preferably highly soluble in a nitrosolvent 
(first liquid), at an elevated but acceptably safe dissolution 
temperature, so as to form a concentrated single phase nitrosolution. The 
upper dissolution temperature is limited by the boiling point of the 
nitrosolvent, or the melting point of the self-explosive, whichever is 
lower, and the degree of safety desired. The dissolution temperature used 
will preferably be in the range from about 80.degree. C. to about 
150.degree. C. By "highly soluble" I refer to a solubility of at least an 
equal part by weight of self-explosive and nitrosolvent, and preferably 
from about 5 to about 50 times as much self-explosive as nitrosolvent, at 
a dissolution temperature above the recrystallization temperature of the 
self-explosive, the dissolution temperature preferably being in the range 
from about 1.degree. C. to about 30.degree. C. above the recrystallization 
temperature. 
A dispersion of surfactant or emulsifier in a second liquid (fuel), 
hereafter referred to as "surfactant-in-fuel", provides the other 
necessary component of the emulsion from which the explosive is derived. 
It is essential that the nitrosolution of self-explosive and the fuel be 
immiscible to form the emulsion, and that it be formed at an elevated 
temperature which is above the recrystallization temperature of the 
self-explosive from the nitrosolution. Further, upon cooling to a 
temperature below the recrystallization temperature, the self-explosive 
will supercool thus preventing the rapid growth of crystals in the mass. 
This supercooling effect permits enough time to shape the emulsion while 
allowing it to cool, without developing deleterious internal fissures and 
voids. 
The range in which the supercooling is observed will depend upon the 
components of the system but will typically be at least 2.degree. C., 
generally from about 5.degree. C. to about 40.degree. C. below the 
recrystallization temperature of the self-explosive. It is the 
supercooling effect that facilitates the growth of discrete crystals, and 
provides the enhanced contact between the components of the explosive. By 
"discrete crystals" I refer to microcrystals ranging from submicron size 
to about 200 microns in diameter such as are formed when an emulsion 
recrystallizes after being supercooled. 
Self-explosives particularly useful in this invention are high energy 
materials such as dinitrotoluene (DNT), trinitrotoluene (TNT), 
1-nitroguanidine, cyclo-1,3,5-trimethylene-2,4,6-trinitramine (RDX), 
cyclo-1,3,5,7-tetramethylene-2,4,6,8-tetranitramine (HMX), 
pentaerythritoltetranitrate (PETN), trinitro-2,4,6-phenylmethylnitramine 
(tetryl) and diamino-trinitrobenzene (DATNB), nitroglycerine (NG), 
nitrocellulose (NC) and nitrostarch (NS). 
The self-explosive is the major component of the explosive composition 
which may be present in an amount in the range from above 50% to about 97% 
by weight of the explosive composition, and preferably from about 70% to 
about 85% by wt of the composition. 
Nitrosolvents useful to prepare the nitrosolution include benzene, toluene, 
xylene, lower alkyl (C.sub.1 -C.sub.6) substituted derivatives thereof, 
and halogenated and nitrated derivatives thereof, particularly bromo- and 
chloroxylenes, and nitroxylenes respectively, nitroparaffins and 
halogenated nitroparaffins which are liquid at the emulsion processing 
temperature, lower alkyl ketones such as acetone and carbon disulfide. 
The nitrosolvent is a minor component of the explosive composition which 
may be present in an amount in the range from about 5% to about 15% by 
weight of the explosive composition, and preferably from about 10% to 
about 15% by wt of the composition. 
Fuels useful to prepare the surfactant-in-fuel dispersion are preferably 
non-self-explosive, such as hydrocarbons, halogenated hydrocarbons but may 
also include glycols, nitroparaffins, and the like, as long as the fuel is 
substantially insoluble in the nitrosolvent. Typically the fuel is 
selected from the group consisting of mineral oils, fuel oils, lubricating 
oils, liquid paraffins, microcrystalline waxes, paraffin waxes, and even 
the foregoing solvents for the self-explosive, provided the nitrosolution 
is immiscible in the fuel, that is, results in at least two phases. 
Preferred fuels are long chain (C.sub.7 -C.sub.26) nitroparaffins, 
halogenated long chain paraffins such as chlorinated paraffins, lower 
alkylene (C.sub.2 -C.sub.6) and dialkylene glycols such as hexylene glycol 
and diethylene glycol, glycol ethers, nitroglycols, and aliphatic and 
naphthenic mineral oils. 
The fuel may be present in an amount in the range from about 2 to about 25% 
by weight of the explosive composition, and preferably from about 3% to 
about 12% by wt of the composition. 
The surfactant or emulsifier suitable for forming the emulsion of 
nitrosolution in the surfactant-in-fuel D-phase is not narrowly critical 
provided it is inert and adapted to emuisify the particular nitrosolution 
and surfactant-in-fuel mixture at a temperature above the 
recrystallization temperature. For example, an emulsifier which reacts 
with the self-explosive is readily identified in the particular instance 
of a TNT solution, by the development of color. Reactions of other 
surfactants or emulsifiers may result in generation of heat, evolution of 
gases, or in some case, formation of precipitates. Inert surfactants or 
emulsifiers are exemplified by ethoxylated long chain linear or aromatic 
alcohols. Other suitable surfactants or emulsifying agents include alkyl 
benzene sulfonates, phosphate esters such as oleyl acid phosphate, 
sorbitan esters, PEG (polyethylene glycol) mono- and diesters, and the 
like. 
The concentration of the surfactant or emulsifying agent is generally in 
the range from about 1% to about 10%, and preferably from about 3% to 
about 7% by wt of the composition in an essentially anhydrous emulsion, 
which in turn consists essentially of first and second liquid phases which 
are immiscible organic liquids. In many instances the amount of emulsifier 
used is equal in wt to the amount of fuel (say, ethylene glycol) of the 
emulsifier is preferably chosen so as to function as a fuel in addition to 
functioning as an emulsifier or surfactant. 
In a preferred embodiment, the explosive composition is formed by gradually 
dissolving self-explosive in hot nitrosolvent until a supersaturated 
nitrosolution is formed. Typically, the nitrosolution will contain from 10 
to 20 times as much self-explosive as there is solvent. The self-explosive 
may be molten and the temperature of the solution maintained well above 
the recrystallization temperature. 
Separately, a dispersion is formed, by dispersing the surfactant or 
emulsifier in the fuel (say, ethylene glycol) and it is heated to a 
temperature equivalent to that at which the nitrosolution is maintained. 
The nitrosolution is then gradually added to the dispersion while 
vigorously stirring, to form an emulsion. The emulsion is maintained above 
the recrystallization temperature of the self-explosive until a 
homogeneous emulsion is obtained. 
After the emulsion is formed, sensitizers, phlegmatizing agents, ballistic 
modifiers and the like may be added as particulate non-reactive additives 
which are essentially insoluble in the nitrosolvent or fuel, and do not 
interfere with the progressive inversion of the emulsion. 
The composition has a thick creamy consistency which consists essentially 
of microdomains (microdroplets) of nitrosolution as the D-phase, in a 
C-phase of surfactant-fuel. The composition thus formed may cool to a 
temperature below the recrystallization temperature of the oxidizer used, 
without recrystallizing. This "supercooling" of the emulsion allows the 
composition to be poured or injected into a cavity at a lower temperature 
than the melting point of the self-explosive. Upon still further cooling 
and aging, the supercooling effect cannot be maintained, the emulsion 
becomes unstable and will invert. 
Destabilization and subsequent inversion results in formation of discrete 
crystals of the self-explosive, gradually forming a mass conforming to the 
shape of the cavity in which it is contained. Microdomains of surfactant 
and/or emulsifier, and fuel phases separate and are interstially (between 
crystals) trapped, as are domains of surfactant-in-fuel. The proportions 
of each phase will vary depending upon the particular choice of components 
of the system. Whether these proportions are unacceptably high may be 
readily determined by routine trial and error such as one skilled in the 
art would expect to undertake under these circumstances. 
It is only because the relative amount of solvent is so small, that the 
presence of the nitrosolution phase in the shaped mass does not 
substantially adversely affect the properties of the explosive. 
Destabilization also results in transformation of the C-phase into a 
D-phase, whether of nitrosolvent or of solvent substantially free of 
self-explosive. The shaped mass is thus a heterogeneous mixture of 
nitrosolvent, fuel, surfactant and/or emulsifier in a crystalline mass of 
self-explosive.

The invention is illustrated by, but not limited to the following example 
in which all parts and percentages are expressed on a weight basis unless 
otherwise specified. 
EXAMPLE 
2028 g of TNT are dissolved in 100 g of hot (about 80.degree. C.) benzene 
with stirring in a round-bottomed flask to form a substantially anhydrous 
nitrosolution. In another flask, 105 g of a polymeric surfactant are 
thoroughly dispersed in 2.10 g of ethylene glycol to form a dispersion 
(fuel phase) which is heated to about the same temperature as the 
nitrosolution, namely 80.degree. C. The hot nitrosolution is slowly 
dripped into the hot dispersion with vigorous agitation so as to form a 
polyphase (two or more phases) mixture (crude emulsion) consisting of 
droplets of nitrosolution dispersed in the surfactant-in-fuel dispersion. 
When all the nitrosolution is added, the crude emulsion is a thick fluid 
containing 83% TNT, 4.1% benzene, 4.3% surfactant and 8.6% ethylene glycol 
(all by weight) The crude emulsion is then refined by high shear mixing 
until a desirable viscosity is achieved. At this point the high shear 
mixing is discontinued and the refined emulsion allowed to cool slightly 
to about 65.degree. C. before transferring it to a molding cavity. Upon 
further cooling to ambient temperature (about 20.degree. C.) a mass of 
contiguous crystals (solid phase) is formed, conforming to the shape of 
the cavity, with minor amounts of liquid phases interstitially distributed 
therein.