Explosives

The invention provides a method of sensitizing a base emulsion of the water-in-oil type, and the invention provides also a sensitized emulsion explosive comprising an emulsion of the water-in-oil type when produced by the method. The method comprises dispersing, in the base emulsion, a sensitizing solution having a solvent which comprises at most 50% by mass water, the balance of the solvent being organic, and a solute which is a chemical sensitizing agent.

THIS INVENTION relates to an explosive. More particularly, the invention 
relates to a method of sensitizing a base emulsion of the water-in-oil 
type to provide an emulsion explosive; and to an emulsion explosive when 
sensitized by the method. 
According to the invention there is provided a method of sensitising a base 
emulsion of the water-in-oil type comprising a discontinuous phase which 
forms an oxidising salt-containing component and a continuous phase which 
is immiscible with the discontinuous phase and which forms a fuel 
component, the method comprising dispersing, in the base emulsion, a 
sensitizing solution having a solvent which comprises at most 50% by mass 
water, the balance of the solvent being organic, and a solute which is a 
chemical sensitizing agent, thereby to form a sensitised emulsion 
explosive from the base emulsion. 
In other words, according to the invention there is provided a method of 
sensitizing a base emulsion of the water-in-oil type (also known as the 
water-in-fuel type) comprising a discontinuous phase which forms an 
oxidizing salt-containing component and a continuous phase which is 
immiscible with the discontinuous phase and which forms a fuel component, 
the method comprising dispersing, in a base emulsion, a sensitizing 
solution having a solvent which is essentially organic, and a solute which 
is a chemical sensitizing agent. 
By essentially organic is meant that the solvent contains no more than 50% 
by mass water, preferably no more than 25% and more preferably no more 
than 12%. By keeping water content at low levels, any undesirable effects 
of water, relating to reduced sensitivity or energy production upon 
detonation, can be resisted. 
More particularly, the base emulsion may be a non-detonable emulsion, the 
solvent having a viscosity of at most 2000 cP at 20.degree. C., the 
organic part of the solvent being capable of acting as a fuel constituent 
in the sensitised emulsion explosive formed from the base emulsion, and 
the solvent comprising at most 25% by mass water. 
The solvent may comprise at least one organic liquid selected from the 
group consisting of dimethyl sulphoxide, dioxan, aliphatic amines, glycols 
and polymers of glycols, the solvent comprising at most 12% by mass water. 
The sensitising solution may comprise at least one chemical sensitising 
agent selected from the group consisting of perchlorates, chlorates, 
nitrates, and nitrites. 
The chemical sensitising agent may be a water-soluble chemical gassing 
agent, the organic part of the solvent being fully miscible with water and 
the dispersing of the sensitising solution in the base emulsion acting, by 
gassing the base emulsion, to reduce the density of the base emulsion at 
25.degree. C. from 1.35-1.48 g/cm.sup.3 to 0.8-1.3 g/cm.sup.3. 
The gassing agent may be sodium nitrite, the continuous phase of the base 
emulsion containing a catalyst for accelerating the gassing, the sodium 
nitrite forming 2-20% by mass of the sensitising solution and 0.03-0.3% by 
mass of the sensitised emulsion explosive, and the organic part of the 
solution comprising at least one liquid selected from ethylene glycol and 
diethylene glycol. In other words, the proportions of base emulsion and 
sensitizing solution used may be so that, when they are mixed, the sodium 
nitrite forms 0.03-0.3% by mass of the emulsion explosive. 
In accordance with the method of the invention the base emulsion and 
sensitizing solution are kept separate until use of the emulsion explosive 
is required, at which stage they will be homogeneously mixed. This is 
conveniently done by pumping them simultaneously along a hose and lance 
into a borehole, at the end of which lance is a static mixing device. 
Accordingly, the dispersing of the sensitizing solution in the base 
emulsion may be by pumping the base emulsion and sensitising solution 
along a hose into a borehole, the solution and emulsion being mixed 
together in a static mixing device in the borehole, the hose feeding the 
base emulsion and sensitizing solution to the static mixing device and the 
sensitized emulsion explosive emerging from the static mixing device into 
the borehole. The base emulsion forms a core which passes along the hose, 
the sensitizing solution being fed into the base so that it forms a 
lubricating layer around the core on the inner surface of the hose, the 
core and layer being mixed together as they issue from the lance into the 
borehole, where sensitizing takes place to provide the explosive. 
According to another aspect of the invention, there is provided a 
sensitised emulsion explosive comprising an emulsion of the water-in-oil 
type having a discontinuous phase which forms an oxidising salt-containing 
component and a continuous phase which is immiscible with the 
discontinuous phase and which forms a fuel component, whenever produced by 
the method of the present invention as herein described. 
As indicated above, the solvent may comprise a single organic liquid, or a 
mixture of organic liquids, and preferably has a viscosity of at most 2000 
cP at 20.degree. C., preferably at most 200 cP, the solvent being capable 
of acting as a fuel constituent in the eventual emulsion explosive. 
Examples of organic liquids suitable for use as the solvent include 
dimethyl sulphoxide (DMSO); dioxane; aliphatic amines, in particular 
diethanolamine and ethylene diamine; and glycols and polymers thereof, 
preferably low molecular weight glycols such as ethylene glycol and 
diethylene glycol. 
While the sensitizing solution may contain, dissolved therein, chemical 
sensitizing agents which alter the oxygen balance as oxidizing agents or 
are explosive or high-explosive in nature, examples being perchlorates and 
chlorates such as sodium perchlorate and chlorate, and alkylamine nitrates 
such as methylamine nitrate, and hexamethylenetetramine denitrate, sugar 
nitrates, the chemical sensitizing agent, instead or in addition, may 
comprise a chemical gassing agent such as a nitrite, eg a metal nitrite 
such as the alkali metal nitrites or alkaline earth metal nitrites, in 
particular sodium nitrite. When sodium nitrite is used, the continuous 
phase of the base emulsion may contain catalysts such as urea, thiourea 
and thiocyanate dissolved therein in conventional concentrations as are 
used with an aqueous sodium nitrite solution, to accelerate gassing. 
Several chemical sensitizing agents may be used together. 
When the solvent of the sensitizing solution comprises water, the water 
will typically be used in proportions no greater than are required to 
ensure effective dissolution of the chemical sensitizing agent or agents 
in the solvent. In this case the organic liquids in the solvent are 
preferably fully miscible with water in the proportions used. For this 
reason, when a water-soluble chemical gassing agent such as sodium nitrite 
is used, the solvent will preferably contain some water and the organic 
liquid in the solvent is conveniently a glycol such as ethylene glycol. 
For safety reasons the base emulsion may be a non-detonable emulsion, for 
example being a non-detonable emulsion classified as such by the South 
African Chief Inspector of Explosives. The sensitizing solution, when 
dispersed in the base emulsion, sensitizes the emulsion, for example by 
acting via a chemical gassing agent such as sodium nitrite to reduce the 
density of the emulsion to render it detonable and to convert it to an 
emulsion explosive. Non-detonable base emulsions of the type in question 
which are sensitized by gassing typically have a density of 1.35-1.48 
g/cm.sup.3 at 25.degree. C., before sensitizing thereof, and, after 
sensitizing thereof, typically provide emulsion explosives which have a 
density of 0.8-1.3 g/cm.sup.3 at 25.degree. C., eg 1.0-1.25 g/cm.sup.3. 
When sodium nitrite is used as the chemical gassing agent, it may be 
present in the sensitizing solution in a proportion of about 2-20% by 
mass, preferably 5-10%. 
Typically, the discontinuous phase will comprise at least one oxidizing 
salt selected from the group consisting of ammonium nitrate, alkali metal 
nitrates, alkaline earth metal nitrates, ammonium perchlorate, alkali 
metal perchlorates, and alkaline earth metal perchlorates. 
Thus for good miscibility of the sensitizing solution with the 
discontinuous phase of the emulsion, organic liquids such as glycols which 
solvate with chlorates, perchlorates or amines (when the latter are used 
to sensitize the base emulsion) are conveniently employed. 
The continuous phase may comprise at least one organic liquid selected from 
the group consisting of mineral oils, fuel oils, lubricating oils, liquid 
paraffins, xylene, toluene, petrolatum and dinitrotoluene, and a 
water-in-oil emulsifier selected from the group consisting of derivatives 
of polyisobutylene succinic anhydride, fatty acid esters of sorbitan, 
mono- and diglycerides of fat-forming fatty acids, oxazoline derivatives, 
alkali- and alkaline earth metal derivatives of fatty acids, soya bean 
lecithin, derivatives of lanolin, alkyl benzene sulphonates, oleyl acid 
phosphate, laurylamine acetate, decaglycerol decaoleate, decaglycerol 
decastearate and polymeric emulsifiers containing polyethylene backbones 
with fatty acid side chains. In other words, the fuel may be selected from 
mineral oils, fuel oils, lubricating oils, liquid paraffins, xylene, 
toluene, petrolatum and dinitrotoluene, or mixtures thereof; and the base 
emulsion will usually comprise one or more suitable water-in-oil 
emulsifiers, examples being derivatives of polyisobutylene succinic 
anhydride, fatty acid esters of sorbitan such as sorbitan sesquioleate, 
sorbitan monooleate, sorbitan monolaurate, sorbitan monostearate, sorbitan 
monopalmitate and sodium tristearate, the mono- and diglycerides of 
fat-forming fatty acids, oxazoline derivatives such as 
2-oleyl-4-4'-bis(hydroxymethyl)-2-oxazoline, alkali- and alkaline earth 
metal derivatives of fatty acids, soya bean lecithin, derivatives of 
lanolin, alkyl benzene sulphonates, oleyl acid phosphate, laurylamine 
acetate, decaglycerol decaoleate, decaglycerol decastearate and polymeric 
emulsifiers containing polyethylene backbones with fatty acid side chains. 
The fuel content of the base emulsion may be 2-12% by mass, typically 3-8%; 
and the emulsifier content of the base emulsion may be 0.5-2% eg 1-1.5%. 
The oxidizing salt-containing discontinuous phase in turn will make up the 
balance of the base emulsion eg 75-98% by mass thereof, typically 90-95% 
thereof, the oxidizing salts amounting to 70-95% by mass of the base 
emulsion, typically 85-93%. Ammonium nitrate usually makes up the major 
proportion of the oxidizing salts, forming 40-90% by mass of the base 
emulsion, typically 40-70%, eg 50-60%, the balance being other oxidizing 
salts such as calcium nitrate, which calcium nitrate in turn can form 
4-70% by mass of the base emulsion, typically 15-60%, eg 15-40%. 
Accordingly, the fuel component may form 2-12% by mass of the base 
emulsion, the emulsifier forming 0.5-2% by mass of the base emulsion, and 
the oxidising salt-containing component forming 75-98% by mass of the base 
emulsion. 
A conveniently used base emulsion comprises an organic fuel, an emulsifier, 
a discontinuous phase comprising water, ammonium nitrate and calcium 
nitrate and, optionally, a flame suppressant salt. Flame suppressant salts 
include potassium chloride, potassium sulphate, potassium dihydrogen 
phosphate, phosphonate salts, sodium chloride and calcium chloride. 
Accordingly, the base emulsion may include at least one flame suppressant 
salt selected from potassium chloride, potassium sulphate, potassium 
dihydrogen phosphate, phosphanate salts, sodium chloride and calcium 
chloride, the flame suppressant salt forming 0.5-15% by mass of the base 
emulsion. Broadly, these constituents may be present in the following 
proportions: 
______________________________________ 
Constituent % by mass 
______________________________________ 
Ammonium Nitrate 40-70 
Calcium Nitrate 4-70 
Water 7-25 
Fuel 3-8 
Emulsifier 0.5-2 
Flame Suppressant salt 0-15 
______________________________________ 
More specifically, these proportions may be: 
______________________________________ 
Constituent % by mass 
______________________________________ 
Ammonium Nitrate 50-60 
Calcium Nitrate 15-40 
Water 8-15 
Fuel 3-8 
Emulsifier 0.5-2 
Flame Suppressant salt 0-8 
______________________________________ 
When the base emulsion contains potassium chloride as the flame suppressant 
salt, its formulation may be: 
______________________________________ 
Constituent % by mass 
______________________________________ 
Ammonium Nitrate 50-51 
Calcium Nitrate 24-26 
Water 9-12 
Fuel 7-8 
Emulsifier 0.5-2 
Potassium Chloride 4-5 
______________________________________ 
A conveniently used sensitizing solution comprises ethylene glycol and/or 
diethylene glycol as the organic liquid of the solvent, water, sodium 
perchlorate as a chemical sensitizing agent and sodium nitrite as a 
chemical gassing agent. A typical formulation of this type is: 
______________________________________ 
Constituent % by mass 
______________________________________ 
Organic Solvent Liquid 
20-40 
Sodium Perchlorate 30-40 
Sodium Nitrite 4-16 
Water 8-40 
______________________________________ 
More specifically, these proportions may be: 
______________________________________ 
Constituent % by mass 
______________________________________ 
Organic Solvent Liquid 
30-40 
Sodium Perchlorate 35-40 
Sodium Nitrite 4-9 
Water 8-25 
______________________________________ 
A particular example is: 
______________________________________ 
Constituent % by mass 
______________________________________ 
Ethylene Glycol 40 
Sodium Perchlorate 33 
Sodium Nitrite 9 
Water 18 
______________________________________

he invention will now be described, by way of a non-limiting illustration, 
with reference to the following Examples. 
EXAMPLE 1 
A base emulsion having the following composition: 
______________________________________ 
Constituent % by Mass 
______________________________________ 
Ammonium nitrate 
71.52 
Water 21.85 
Acetic Acid 0.16 
Sodium Acetate 0.09 
Thiourea 0.38 
Fuel Oil Blend 5.00 
Emulsifier 1.00 
______________________________________ 
was admixed with a sensitizing solution having the following composition: 
______________________________________ 
Constituent % by Mass 
______________________________________ 
Ethylene glycol 35.00 
Sodium perchlorate 40.00 
Water 20.00 
Sodium Nitrite 5.00 
______________________________________ 
at a mixing ratio of base emulsion: sensitizing solution of 95:5, the 
solution had a density of 1.07 g/cm.sup.3. The explosive was found to be 
initiable in 44 mm internal diameter PVC tubing, using a detonator 
containing a base charge of 760 mg pentaerythritol tetranitrate (PETN). 
By contrast, in a control test using the same proportions of constituents 
but using the same mass of water, as is conventionally the case, as the 
solvent for the sodium nitrite in the sensitizing solution instead of the 
ethylene glycol/water mixture containing dissolved sodium perchlorate, 
initiation could not be obtained using the same detonator. Instead, a 30 g 
PENTOLITE booster available from AECI Explosives Limited in South Africa 
was required for initiation. 
A theoretical calculation of the energies of the sensitized emulsions 
showed the emulsion containing the ethylene glycol/sodium 
perchlorate/water/sodium nitrite sensitizing solution to have 7.5% greater 
energy than that containing the sodium nitrite/water sensitizing solution. 
EXAMPLE 2 
Example 1 was repeated using the same base emulsion and sensitizing 
solution compositions, but the level of addition of the sensitizing 
solution was increased to 7:93 to provide a lower density emulsion product 
(0.93 g/cm.sup.3). 
The sensitized emulsion was initiable in a 32 mm internal diameter paper 
sleeve using a detonator containing a 760 mg base charge of PETN. 
In a control test using the same proportions of constituents but using the 
same mass of water as the solvent for the sodium nitrite in the 
sensitizing solution instead of the ethylene glycol/water mixture 
containing dissolved sodium perchlorate, initiation of the sensitized 
emulsion could not be obtained in the same diameter cartridge with the 
same detonator, or even with higher strength initiators such as ANSTART 
(1.7 g PETN). 
A theoretical calculation for the energies of the sensitized emulsions 
showed the emulsion containing the ethylene glycol/sodium 
perchlorate/water/sodium nitrite sensitizing solution to have 12.8% 
greater energy than that containing the sodium nitrite/water sensitizing 
solution. 
It is to be noted with regard to the Examples that increased provision of 
sensitivity by the sensitizing solution relative to aqueous sodium nitrite 
sensitizing solutions, and more efficient mixing between the base emulsion 
and sensitizing solution were observed. Furthermore, it was observed that 
emulsion explosives sensitized in accordance with the Examples required 
lower pumping pressures to pump the same volumes, than those sensitized 
with an aqueous gassing solution similar to the control of Example 1. 
It is further to be noted that larger amounts of the sensitizing solution 
in accordance with the present invention may be added to a base emulsion 
without having unacceptably detrimental effects on the energy upon 
detonation of the emulsion explosive. Increases in energy produced upon 
detonation of up to 15% have been noted, compared with the same base 
emulsion sensitized using an aqueous sodium nitrite sensitizing solution. 
Finally, higher bubble energies have been noted, increased by 5-10%, 
compared with the same emulsion when sensitized using the same proportion 
of aqueous sodium nitrite sensitizing solution, to obtain an explosive 
density of 1.2 g/cm.sup.3.