Chapter 1 dissertation on insensitive highly energetic materials by theodore s. ted sumrall
CHAPTER – 1
Uses for Commercial Explosives
Commercial explosives are used in a number of applications, including coal mining,
blasting of rocks, etc. It is desirable that explosives combine their efficiency in executing
certain work with economy and safety. Many of the older types of explosives are based
on NG (such as Dynamites), but the trend in modern explosives has been to reduce the
amount of NG by replacing NG with other, less expensive components. The majority of
modern commercial explosives contain AN and some combustible material such as
charcoal, coal, coal tar, or petroleum products.
A typical example of a modern, inexpensive commercial explosive is the Ammonium
Nitrate-Fuel Oil (ANFO) described by Cook . Many commercial explosives designed
for certain types of work may also be used for other purposes as detailed in Table 1-1
Commercial Blasting Applications For Explosives 
Blasting Ice Jams
Oil Well Stimulation and Penetration
Construction Work inc. grade construction and pipelines
Metallic Mines (Ore)
Nonmetallic Mines: Limestone, clay, gypsum, salt, potash, talc,
Open Pit Mining
Worldwide, explosives used in coal mines are the most important and numerous of all
commercial explosives. They are employed for breaking coal or rock in mines.
Explosives used for breaking coal should be of low brisance, but possess “heaving
properties”, so that the coal will be broken in rather large lumps without pulverizing it.
Addition of aluminum powder has been demonstrated as a proven method for decreasing
the brisance of a high explosive while increasing the pressure pulse duration and overall
effectiveness of explosives requiring low brisance and high overall blast pressure.
Although classified as a “non-permissible” explosive (i.e. not permissible for usage in
underground coal mines which contain volatile gases) aluminized explosives are still quite
suitable for blasting coals either containing no volatiles (such as anthracites) or
containing little of them (such as semibituminous coals). These explosives are also
suitable for use in blasting rock in coalmines. [2,3]
One of the requirements of any explosive used in underground mines is to possess a
positive oxygen balance to CO2. This is in order to avoid the formation, on explosion of
CO, which is extremely toxic and can form with air explosive mists. In this respect,
neither K or Na oxidizer is an ideal oxygen supplier for mining explosives, because the K
or Na Radical fixes oxygen, forming K2O or Na2O . Ammonium Nitrate (AN) and
Ammonium Perchlorate (AP) are very suitable due to the superior oxygen balance of
both. The price for AN in the 19th Century was too high for use in mining explosives.
Only after 1920, when the synthetic nitrogen industry had been established and the price
of AN dropped, did it become possible to use AN in many “permissible” NG based coalmining explosives. Currently, AP is more expensive than AN, however, research by the
early part of the next century should drop the price of AP in the same manner as the price
of AN has dropped.
Explosives used in blasting operations (such as in quarry work, non-gaseous mines,
strip-coal mines, metal mines, ditching, hole drilling or in the demolition of buildings,
roads, bridges, railroad tracks, sunken ships, under water obstacles in channels, etc.) are
classified as blasting explosives. TNT and NG /Gelatin based Dynamites are among the
explosive materials used for commercial blasting and demolition work. The short
duration and low temperature of detonation required for permissible explosives are not
required in most blasting operations.
The principle factors which govern the selection of a commercial blasting explosive are:
power; detonation pressure (also called brisance); density; sensitivity; stability; waterrepellence; and cost. These factors assume varying degrees of importance according to
the circumstances under which the explosive is to be used. For blasting very hard rock
(such as gold quartz) a very powerful and brisant explosive is required. As underground
drilling is expensive, the density of the explosive should be high. TNT and blasting
gelatin are suitable for such purposes. TNT is readily initiated with even a small booster.
Blasting gelatin requires initiation with a detonator powerful enough to produce a
detonation velocity of approximately of 7000 m/sec. In quarrying and strip-mine
operations where the work is done in the open, large drills are used and explosive
charges from ≥ 10-15 cm diameter are required. For such work, TNT, either alone or in
composite explosives is very suitable.
For under-water blasting (i.e. harbor/channel/port construction, channel clearing, and
etc.), waterproof explosives such as TNT, Gelatin Dynamites, or Pentolite (50/50
TNT/PETN) has been used. It should be noted for underwater explosives, the effect
produced is considerably less than it would be on land due to the pressure of the
surrounding water. Thus, high performance explosives (such as TNT) are essential.
Major Energetic Material Incidents 1900-1997
A number of explosive accidents have claimed an estimated 15,000+ lives during the 20th
Century. Table 1-2 lists 13 major accidental explosions described in available literature
[5,6,7]. It is important to note that a higher percentage of fatalities per mass of explosive
is observed in high population density areas such as Japan. As an example, the majority
of the people killed from an explosion which took place in Yokohama, Japan in 1959 were
passengers in a train that was passing by a TNT plant at the moment of the explosion.
Some Energetic Material Related Fatalities (1900-Present)
1 km/2.5 km
New JerseyU 1.0
J = Japan, U = USA, C = Canada, G = Germany, P = PRC, F = France,
The most striking fact in this tabulation is that a number of these greatest explosions
involved one of the least sensitive of all explosives, namely Ammonium Nitrate (AN). The
Texas City explosion was actually two fertilizer-grade AN explosions, one on the
steamship Grand Camp and the other the following day on the steamship High Flyer
(Figures 1-1 through 1-6). The Brest, France explosion also involved another shipload of
AN. These cases illustrate the hazards involved whenever the explosive properties
of even a very insensitive explosive are overlooked, especially under conditions where
the charge mass exceeds a certain critical value. [1, 7, 8]
Previous Related Studies
Early Attempts at Desensitizing Energetic Materials (Pre-1800)
Prior to 1800, the overwhelming majority of energetic materials in use for mining
applications consisted almost solely of black powder. According to Dutton a Hungarian
engineer, Kaspar Weindl, experimented in blasting ore near the town of Selmeczbanya
by means of Black Powder in 1627. . From that time, use of Black Powder for breaking
ores spread to Germany, Sweden and other countries. According to Marshall, blasting
was probably introduced to England in 1670, and in 1689 Epsly started to use Black
Powder in Cornish mines.  However, as black powder was a very weak explosive,
attempts were made during the 19th Century to replace it with something more powerful.
One of such attempts was the invention of Berthollet Powder which consisted of 75%
potassium chlorate, 12.5% sulfur, and 12.5% charcoal. This mixture was more powerful
than black powder, but it was extremely sensitive and for this reason was very
dangerous.  Several other mixtures were proposed but none proved to be suitable for
industrial purposes. Owing to the much greater desire for improved performance,
insensitivity and safety were of much smaller concern and negligible attempt was made
to improve the safety characteristics of black powders.
Early Attempts at Desensitizing Energetic Materials (1800-1900)
The 19th Century brought about the invention and/or use of other explosives, including
Picric acid (PA), trinitrotoluene (TNT), nitrostarch (NS), nitrocellulose (NC), and the very
powerful but sensitive nitroglycerin (NG). Owing to its very low cost, high power and
ease of manufacture, NG literally dominated the latter half of the 19th Century as the
explosive of choice. However, as is widely known, NG is very sensitive and significant
attempts were made to decrease the sensitivity of NG as detailed below.
The first important invention before the invention of NC or NG was the preparation in
1833 of impure nitrostarch by Braconnot. In 1846, NC was prepared with a high nitrogen
content independently by C.F. Shonbein (1799-1866) and F. Bottger (1806-1886). 
In 1846, NG was prepared by the Italian chemist Ascanio Sobrero (1807-1867). NG
proved to be more powerful than any previously prepared explosive. Because of the
extreme sensitivity of NG, its use on a large scale was considered to be dangerous and
the fact that it was liquid made it difficult to transport or to handle. It was nearly
impossible to use NG in horizontal boreholes, but when used in vertical boreholes, there
was a danger that NG might run into surrounding fissures in the rock, escape the
detonation of charge, and either burn (giving deleterious nitrogen oxides) or, if unburned,
remain a grave source of danger during removal of the rock by mechanical means.
Attempts were made to overcome this difficulty by lining the boreholes with wet clay, but
this was time consuming and not always effective. 
However, NG in liquid form found extensive use for blasting oil wells in Pennsylvania
USA where the petroleum industry started to develop in the middle of the 19th Century.
Straight NG was also used in construction of tunnels at this same time.
Before inventing his dynamite in 1863, Alfred B. Nobel (1833-1896) proposed a safer
method of transporting liquid NG by mixing NG with 15-20 parts of anhydrous methanol
and transporting the resulting non-explosive mixture in tanks to places of work. At the
work site, NG was precipitated by adding water and the supernatant dilute methanol was
removed by de-cantation. However, as this method was time-consuming and rather
wasteful (because it did not pay to recover methanol), it was seldom used in the USA,
where everything is done in a hurry and as cheaply as possible. It was therefore
preferred to transport NG in the liquid form in the US, although, it was more dangerous.
Many accidents occurred and many lives were lost in connection with NG. As long as
most of the workmen were foreigners, the industrialists, who card only for profits, did not
introduce any safety regulations until they were forced by the US Government after
establishing the Bureau of Mines in 1910. As accidents with NG continued to occur,
some countries, among them Great Britain, prohibited its manufacture and use beginning
about the middle of the 1860’s. However, despite a number of accidents, Dynamite
began production in the US in 1868.
The first US Dynamite plant was constructed in California at a spot called Rock House
Canyon, near San Francisco. It was operated by Chinese, but the supervisors were
American. The plant, consisting only of shacks, was called the “Giant Powder Co”.
Great opposition to Dynamite was encountered from a plant constructed in Santa Cruz,
California, “The California Powder Works”, manufacturers of black powder. However,
when the Great Comstock Gold Lode was discovered, black powder proved to be too
weak to blow the hard rock of Mt. Davidson and only Dynamite could do it. The
increased demand made the management of Giant Powder Co. push their Chinese
workers harder and harder to meet the demand, and as a result of this hurry, the plant
blew up in November 1869, killing two Americans and all of the Chinese employees. This
accident did not discourage Nobel Co., and another larger and safer plant was
constructed. A large Chinese crew was assembled and a German chemist was sent from
Europe as Superintendent. The first 23 years of Giant Company exemplify in dramatic
terms the introduction of Dynamite in the US. During that period, five successive plants,
each larger than the pervious ones, were wrecked by explosions and in all 83 people
(mostly Chinese) were killed. 
Prior to the discoveries by Nobel, a number of researchers attempted various methods to
desensitize NG. In 1854, introduction of the earliest Dynamite called Magnesial’nyi was
produced by the Russian officer V.F. Petrushevskii. It consisted of NG absorbed by
powdered magnesit or magnesia. It was used in Siberia for blasting in gold mines..
Also, there was a claim in the literature  that previous to the discovery by Nobel of
Guhrdynamit (1867), a German mining engineer, F. Schell of Clausthal, Oberharz, used
as early as 1866, a mixture of NG and crushed “Pochsand” (ore sand) for blasting in
mines of the Harz Mountains. After visiting Schell in 1866, Nobel found out that
kieselguhr would make a better absorbent for NG than Pochsand.
Prior to the discovery of Guhrdynamit, Nobel, who started to work as early as 1862 on the
search for a suitable absorbent for NG, prepared a charge consisting of a cartridge made
from Zinc foil filled with pulverized black powder impregnated with NG. Such cartridges
were successfully detonated under water and British Patent No. 2359 was obtained in
1863 for their manufacture. Manufacture began at Emmanuel Nobel’s plant in
Helenborg, Sweden but was stopped in the fall of 1864 when a great explosion took
place, killing Alfred’s youngest brother and a chemist employee.
Because black powder was not a good absorbent for NG and the mixture was not safe in
transportation, Nobel started to investigate other possible absorbents. In 1865, Nobel
succeeded (after trying the following as absorbents for NG: charcoal; silica, powdered
brick; and shredded paper) in finding a good porous material, known as kieselguhr, guhr,
or infusorial earth. When pulverized, it could absorb up to four times its weight of NG.
On the strength of this he compounded a mixture of 75% NG with 25% guhr. This
mixture proved to be satisfactory not only from a safety standpoint but also in its
explosive properties, being less sensitive to shock but more readily detonable than liquid
NG. Alfred Nobel called the new explosive Dynamit, derived from the Greek word
“dinamis”, which means force. This particular explosive became also known as
“Guhrdynamite” and “Dynamit No 1” or “Kieselguhr Dynamit”.
Theodore Winkler, an associate of Alfred Nobel, made (in 1868 near San Francisco, CA)
3 pounds of Dynamite by mixing 1 part of Kieselguhr with 3 parts of NG. He used the
facilities of Judson & Sheppard Chemical Works of San Francisco and then
demonstrated the strong action of this new explosive by blasting boulders along the line
of Bay Shore Railroad. 
None of the Dynamite plants constructed before 1873 in the USA belonged to DuPont &
Co., the leading manufacturer of black powder. There were two reasons for this:
dangers in transportation of NG; and higher prices of Dynamites in comparison with the
new black powder formula introduced in 1857 by Lammot DuPont.
Although Guhrdynamite proved to be a good, inexpensive explosive (and it is still used in
some parts of the world, although discontinued in the USA since 1908) its disadvantage
was that it contained 25% inert material (kieselguhr) which did not participate in the
explosion. To overcome this disadvantage, Abel in England and Trauzl in Austria
proposed in 1867 the usage of NC as an absorbent for NG. As the NC in use by then
had a higher Nitrogen content than Collodin Cotton, it could not be coloided by NG and
explosives prepared by this method were not of the gelatin-type but powdery. As their
NC was not a good absorbent for NG, explosives of Abel and Trauzl were exudable and
for this reason not successful. Schultze of Prussia patented in 1868 an explosive
consisting of NG and partly nitrated wood (nitrolignin) but this explosive, known as Dualin
also exuded NG and for this reason was considered unsuitable.
During the time of Nobel’s research towards discovery of a suitable absorbent for NG,
pulverized sand was proposed by Prof. Seely and mixtures of pulverized AN with
sawdust or charcoal were proposed in 1867 by Swedish inventors Norrbin and Ohlsson
and also by Bjorkmann. When these mixtures were combined with NG, Dynamite-like
explosives Ammiakkrut and Seranin were obtained. . The Seranin explosive
(developed by Bjorkmann and patented in 1867) consisted of 18.12% NG, 72.46% AN,
8.7% sawdust or charcoal. This formula was distinct from the Seranine explosive
developed by Horsley, which consisted of 27% NG absorbed by a mixture of pulverized
potassium chlorate, gall nuts, alum and magnesium sulfate. 
Although Nobel knew at the time of invention of his Dynamite about advantages of AN
addition, he could not use it in his Dynamites because AN based dynamites were already
patented by Norrbin and Ohlsson. So he decided to purchase their patent in 1870. This
patent covered the explosives containing 80% AN, 10%-14% NG and 6%-10% charcoal.
As this explosive was hygroscopic, he coated the particles of AN with paraffin (Stearin,
ozokerite or naphthaline), thus practically eliminating its hygroscopicity. For this
explosive Nobel was granted British Patent No. 1570 (1873).
Previous to this, Nobel worked on explosive mixtures consisting of NG partially absorbed
by mixtures of combustible materials (such as woodmeal, charcoal, rosin, sugar, starch,
etc.) with oxidizers (such as potassium or sodium nitrate) and was granted British Patent
No.442 (1869). These explosives, as well as Amoniakrut and Seranin, served as
prototypes for explosives known in the US as “Ammonia Dynamites” or ”Ammonium
Nitrate Dynamites”. These Dynamites are still in use in the Western Hemisphere. 
In 1870, an American chemist (James Howden) proposed a Dynamite consisting of 75%
NG absorbed by 25% of a mixture consisting of pulverized sugar, potassium nitrate and
magnesium carbonate. This Howden’s Dynamite was stronger than corresponding
Guhrdynamite and was first employed in 1872 on the first big Dynamite job, which was
the driving of the Musconetcong tunnel, 1 mile long, near Easton, Pennsylvania on the
Easton and Amboy Railroad (currently the Lehigh Valley Railroad). [2,20]
The next step in the Dynamite industry was replacement of straight NG with NG
gelatinized with Collodin Cotton, which is NC consisting of approximately 12% Nitrogen
rendering explosives known as Gelatin Dynamites or simply Gelatins . The strongest
of these explosives were Blasting Gelatins. British Patent 4179 was granted in 1875 for
both types of Dynamites. The last patent granted to Nobel on Dynamites was in 1879.
That was for Ammon-gelatin or Ammonium Nitrate Gelatin. 
Meanwhile, Alfred Nobel, with the assistance of his father, Emmanuel (1801-1872), was
engaged in attempts to utilize NG in explosives and improve its method of preparation,
naming their product Pyroglycerin or Glonilol. It became later known as Nobel Sprengol.
Other inventions of note during the 19th Century were nitroguanidine (NQ), which was first
prepared by Jousselin in 1877. NQ did not begin to be widely used until the turn of the
century at which time it was used more for propellant applications than as an explosive
owing to its cool burning characteristics and insensitivity to shock . In 1880, TNT was
made in a very pure state by P. Hepp. 
In 1888, a now well-known, very insensitive high explosive (IHE), tri-amino-trinitrobenzene (TATB) was first prepared by Jackson and Wing. In 1928, the process was
further refined by Flurscheim and Holmes . Unfortunately, high production costs
prevent this almost ideal explosive from enjoying wide spread usage today.
In 1899, cyclo-trimethylene-trinitramine (RDX) was first prepared by Henning of Germany
who named it Hexogen and used it for medical purposes. Then Brunswig prepared RDX
in 1916, but it was not until 1920 that its’ explosive value was recognized by Eric Von
Herz. The first person who prepared it in fairly good yield was G.C. Hale in 1925. Little
additional research was conducted until 1940 when J. Meissner of Germany developed a
continuous method for RDX manufacture . Though more powerful than NG, RDX is
less sensitive than NG (but still considered sensitive, however, not as expensive as
Contemporary Attempts at Desensitizing Energetic Materials (1900-1950)
Commercial efforts to desensitize explosives during this period of time principally
concentrated on research in the area of freezing point depressants for NG. The early
high-explosives era was plagued with many accidents associated with thawing of frozen
NG in dynamites. Freezing renders dynamites relatively insensitive, and they therefore
had to be remelted before they could be used in blasting operations. Since NG freezes
at +13 °C, it is natural that Dynamites containing NG will freeze in cold weather. This is
very undesirable because such Dynamites become so hard that a blasting cap cannot be
inserted in cartridges and the NG becomes somewhat insensitive to initiation. Such
cartridges cannot be detonated, even when using the strongest cap available, but require
a booster. Although frozen cartridges can be detonated (with difficulty), they should not
be used without defrosting prior to usage. Since all the prescribed methods of defrosting
are time consuming, attempts to speed-up thawing almost always resulted in accidents.
The safest method was therefore to incorporate a freezing point depressant in NG in
order to produce a Dynamite which did not freeze in cold weather. Because many of the
attempts with addition of antifreeze resulted in either failure or lower performance,
manufacturers ignored this drawback and continued to use NG without antifreeze. This
continued until 1902 when a severe explosion in Greisenau Mine, Germany occurred
caused by frozen Dynamite. This disaster produced the renewal of research on
antifreezes and 1903, the SA de Poudres et Dynamites of France introduced DNT and
TNT as antifreezes. Various melting-point depressants for NG were studied, some of the
most interesting of which were mono-nitrotoluene (MNT) and di-nitrotoluene (DNT).
Other solutions to the problem were made by Kast who discovered in 1906 the isomeric
forms of NG, and in 1911 by Woodbury, who disclosed the nitration of mixtures of
glycerin and sugar . While the addition of DNT and TNT did not result in performance
loss, unfortunately it still did not suppress the freezing point of NG to desired ranges.
Since this time, a number of antifreeze additives were investigated with the most
successful being principally nitrated alcohols. The most important antifreeze (prior to
1950) has proven to be ethyleneglycoldinitrate (EGDN). The commercial introduction in
1911 of nitrated mixtures of glycerin and ethylene glycol (producing NG and EGDN)
provided the most satisfactory solution of this important problem. Today commercial NG
is manufactured as a mixture of NG-EGDN. The explosive properties of EGDN are
almost identical to those of NG, as also are those of the low-freezing mixture, the only
significant difference being the melting point.
One other invention which bears mentioning is the “Continuous Nitration Process”
(developed by Agne Nilsson and Bemt Brunnberg) which permitted the continuous
manufacture of NG, rather than conventional “Batch Mixing”. This minimized the amount
of NG in the plant at any one time such that if an explosion did occur, only a minimum
amount of NG would be involved in the incident. 
Modern Attempts at Desensitizing Energetic Materials (1950-1997)
A number of explosives have been developed during the latter half of the 20th Century in
order to help: increase performance; decrease cost; and decrease the sensitivity of
explosives and thereby decrease the risk of fatalities. Four types of explosives are worthy
of mention: Ammonium Nitrate/Fuel Oil (ANFO), Slurry Explosives, Emulsion Explosives
and Plastic Bonded Explosives (PBX).
Slurry Explosives and Emulsion Explosives both derive a higher degree of safety due to
the presence of water in the compositions. Additionally, slurries and emulsions can be
manufactured as both high explosives and blasting agents. The Bureau of Explosives
and the Department of Transportation differentiate between high explosives and blasting
agents as follows. A high explosive is one that detonates with a No. 8 blasting cap at 21
ºC. A blasting agent is one that fails to detonate with a No. 8 cap at 21 ºC, and passes
electrostatic discharge, burning and differential thermal analysis tests. AN is actually
shipped as an oxidizer despite its explosive properties.
Development of ANFO
While slurries and emulsions are patented inventions, ANFO generated spontaneously
outside the explosives industry, even under an initial strong opposition by the industry.
Four stages of this evolution may be cited:
The prilled AN or Fertilizer Grade AN “FGAN", unique to ANFO, was developed in the
early 1940's as a fertilizer initially rejected for use in explosives as too coarse, high in
moisture, and low in density. "Explosive-grade" AN is nonporous and nonfunctional in
ANFO except in very fine mesh sizes.
FGAN explosion catastrophes in 1947 at Texas City and Brest (France), and later that
year in the Black Sea, left the lasting impression on the public, particularly mine operators
then paying high prices for explosives, that AN is a low-cost, powerful explosive with
good blasting potential which was somehow overlooked by the explosives industry.
Under this erroneous impression, mining engineers attempted (in the mid-1950's) to use
FGAN directly as a blasting agent in the large boreholes of the iron ranges of Michigan
and northern Minnesota. The mining engineers did not realize that the product available
to them was a slightly desensitized form of AN which was distinctly different from the
(sensitized) FGAN involved in the catastrophes. These early attempts were still not
entirely unsuccessful owing to the explosive ability of pure AN and its use in large
boreholes with multiple boostering by large dynamite charges. Do-it-yourself efforts
finally became successful when operators, after learning that fuel is needed to sensitize
and strengthen AN, began to use about a gallon of fuel oil along with each bag of AN.
An important symposium held in October 1956 at the University of Minnesota brought
together mining engineers and explosives scientists who then joined forces in the
characterization, mechanization, and standardization of the ANFO system.
The products that detonated in the accidental explosion of FGAN were coated (for anticaking purposes) with nearly 1.0 % wax which was good for the intended purpose but
unfortunately is also a good fuel-sensitizer for FGAN. By strange coincidence, this
amount of the coating gave a (sharp) maximum explosive sensitivity. Even the oxygenbalanced 94.5/5.5 AN/wax composition was appreciably less sensitive. The relatively
high sensitivity of the wax-coated FGAN, along with the large charge size factor (the
shipload explosions involved 3 x 106 to 4 x 106 kgs of FGAN in each case), explained
how the FGAN was able to undergo sudden transition from deflagration to detonation in
each of the shipload conflagrations. But it did not explain how the fires were initiated.
The explanation developed in the litigation seems conclusive. The FGAN was bagged
and shipped hot (at 33ºC ± 11ºC). the paper bags often became AN impregnated in
exposure to moist and wet conditions, and, while wax coatings do not lower the thermal
stability of AN, Findlay and Rosebourne had found 25 years earlier that celluloid
materials in intimate mixtures with AN do lower its thermal stability. In fact, the AN-paper
combination self-heats in the very temperature range used in bagging and shipping the
FGAN. Indeed, it often arrived at the seaport appreciably hotter than when it was
bagged. Bag embrittlement and even charring by self-heating caused excessive spillage,
re-bagging, and contamination. Furthermore, several spontaneous fires in rail transit of
the product preceded the Texas City catastrophe. After this disaster the wax coating was
replaced by kieselguhr, a somewhat inferior anticaking agent but a safe one. It was this
(desensitized) guhr-coated FGAN that mine operators used in the ANFO development.
When sensitized with about 6% paraffin or Fuel Oil (FO), ANFO is the cheapest source of
explosive energy in the modern world. This has long been recognized, and considerable
research has gone into finding how to use it even more effectively in ever-increasing
amounts. While the annual consumption of AN in commercial explosives was relatively
small in the period 1912 to 1928, it attained greater prominence in the industry with the
invention of Nitramon, a high AN, non-NG explosive developed by Du Pont [29, 30].
Though contributing immensely to industry for two decades, Nitramon, like dynamites,
quickly gave way to modern blasting agents ANFO and slurry.
So significant have been the modern blasting agents, ANFO and slurry, to open-pit
mining that the entire commercial explosives industry suddenly expanded some five
times relative to the zenith of the dynamite era. The tremendous expansion was
triggered by the new economies made possible by blasting agents and other open-pit
mining technologies. Indeed, the great taconite industry probably would not have been
economically sound without the slurry development, a claim made by leading taconite
operators. Several important advantages are responsible for the great success of ANFO:
(1) ANFO is yet the cheapest source (by weight) of explosive strength (explosive energy
per gram) in the modem world; (2) It is orders of magnitude safer than dynamites, yet not
as safe as slurries or emulsions; and (3) Porous, prilled AN readily absorbs and retains
the proper amount (6%) of fuel oil. ANFO is easily mixed and loaded into the bore-hole
by fast and efficient mechanical methods. A great advantage of ANFO, slurries, and
emulsions is that as bulk rather than packaged explosives they fill the bore-hole
completely, a feature now recognized to be of great importance in blasting efficiency.
The remarkably simple ANFO mixture found use at first only in the large-diameter
boreholes of open-pit blasting but a few years later became popular in small-diameter,
underground blasting as well. This was made possible by blowing it into the small
boreholes under sufficient pressure to break down the prills and reduce the critical
diameter below the (small-diameter) bore-hole size. (Before this high-pressure loading,
ANFO has a critical diameter of four to five inches.) Only two deficiencies prevented
ANFO from taking over almost the entire commercial explosives market: (1) It is readily
desensitized by water and therefore generally cannot be used under adverse water
conditions characteristic of an appreciable part of commercial blasting. (2) In spite of
complete filling of the bore-hole, it is low in density and develops too low a pressure in
the bore-hole (“bore-hole pressure") to break successfully the hardest rocks, particularly
at the bottom or "toe" of the burden and in "tight" blasts where breakage is most difficult.
 ANFO has a calculated detonation velocity of approximately 3900 meters/second at
a density of 0.82 g/cm3. This translates to a detonation pressure of only 31 kbars.
Despite the low costs associated with ANFO, the performance is almost 8 times below
the target detonation pressure of 240 kbars.
The AN currently used in blasting is formed into a porous pellet called a prill. A mixture
of 94.5% AN and 5.5% fuel oil (by weight) was found to be the most efficient explosive
and is termed ANFO. The addition of fuel oil allows all the available oxygen from the AN
to be used effectively in the explosion. Unfortunately, ANFO is not without several
drawbacks, including its low density and its hygroscopicitiy. Paradoxically, it was found
that through the addition of water, with suitable stabilizing agents, and if desired, gelling
agents, not only are most of these problems overcome, but the handling of the explosive
is simplified. These water-based slurries or gels vary in consistency from a heavy paste
or jelly to a solid rubbery mass, depending on the gelling agents used. The most
common agent is a gum such as guar. The gelling agent serves two purposes: 1) it
ensures a homogeneous mixture by preventing settling of components, and 2) it
A simple slurry is one in which the fuel oil found in ANFO is replaced with another fuel
which is compatible with a water gel. Most commercial slurries consist of an explosive
base (such as AN or Sodium Nitrate (SN)) and a fuel such as carbon, Sulfur or aluminum
powder. The addition of large quantities of aluminum produces a slurry with very high
energy release at moderate detonation pressures. Advantages are ease of field use, less
sensitivity to heat and shock, void-less filling of holes and low expense. Disadvantages
are: low density and thus low performance and/or the need for a large booster charge for
initiation, and long term storage limitations. These booster charges, however, are
typically manufactured from much more sensitive explosives such as TNT or TNT/PETN.
Development of Slurry Explosives and Blasting Agents
The fundamental concept of Slurry Explosives (SE) and Slurry Blasting Agents (SBA)
was that a saturated aqueous oxidizer (primarily AN) solution is used as the continuous
or dispersion phase of a slurry to disperse both excess solid oxidizer and the sensitizing
fuel. While usually insensitive to commercial detonators, slurries propagate detonation
satisfactorily, particularly in the large diameter boreholes of open pit mines, when initiated
with sufficiently powerful boosters. "Fuel" is used here in the generic sense as any
combustible material, whether explosive or not, that can be uniformly dispersed in the
slurry medium. It may include oxygen-deficient explosives like TNT, Composition B, or it
may comprise non-explosive fuels such as hydrocarbons, carbonaceous and cellulose
materials and combustible, heat-producing metals, i.e., Al and silicon. As they contain
significant amounts of water, SE and SBA are among the safest of all explosives (in the
final state) because they are not easily ignited and are somewhat insensitive to most
types of shock (i.e. bullet impact and friction) that can initiate the explosion of dynamites.
Furthermore, they are made water-resistant by means of the hydrophilic colloidal guar
gum. However, because aluminized slurry explosives contain a significant amount of
water, over time the water (in conjunction with AN) reacts with the Aluminum often ending
with an unintended detonation. Additionally, as high temperatures are required to ensure
that all of the oxidizer is dissolved, self heating type explosions have been known to
occur with both slurry and emulsion explosives and blasting agents . Also, while
slurry explosives may be less sensitive than dynamites to shock, they will most certainly
fail fragment impact due to the shock properties associated with the fragment impact test
and the fact that slurry explosives are cap sensitive and therefore, Class 1.1 explosives.
Blasting agents are those based entirely on non-explosive ingredients and are insensitive
to commercial detonators or blasting caps and require boosters to detonate them.
Nitramon was the first slurry blasting agent explosive. One grade consists of simply AN
and paraffin and was thus similar to ANFO except for use of a solid rather than a liquid
fuel and a metal container.
The aluminized slurry blasting agent, or SBA, was discovered in 1956. TNT slurry
explosives, which were discovered in 1957, gained immediate commercial importance by
virtue of excellent reproducibility and ease of manufacture. SE-TNT is singularly useful in
high pressure applications, i.e., deep well and underwater blasting. SBA-Al and SETNT/Al with high Al contents (up to 35%) are some of the most powerful of all commercial
SBA-fuel types are the lowest in density and strength of the slurries but also have the
lowest ingredient costs. They are therefore useful mainly as toploads and for wholecolumn loads in relatively soft rock. They are also less sensitive than slurry explosives to
SE and SBA have captured much of the open-pit blasting market because they are
singularly applicable in very hard rock as bottom loads and in all types of rock under
difficult water conditions. High loading densities (relative to ANFO) and bulk strengths
characteristic of SE and SBA, permit lower drilling costs, higher blasting efficiencies, and
better rock fragmentation. Savings are effected therefore in labor, drilling, digging,
hauling, crushing, and grinding. Scientific field-cost comparisons between SBA and
ANFO conducted in even dry, soft rock where ANFO works best have sometimes even
favored SBA . However, slurries still suffer from a number of drawbacks. Due to the
high water content of slurries, they have much lower densities that TNT based
compositions. This translates to lower performance. Also, as stated previously,
according to the inventor of slurry explosives, aluminized slurries and slurry blasting
agents should not be stored for more than 1 year at ambient temperature due to the
reaction between AN, water and aluminum. Additionally, continuous heat dissipation is
necessary when manufacturing even non-aluminized slurries and emulsions to prevent
self heating and detonation of slurry and emulsion explosives and blasting agents .
Slurry explosives are still considered shock sensitive (Class 1.1) and both slurry
explosives and slurry blasting agents are 350% to 550 % lower in performance (with
regards to detonation pressure) than the target goal.
Development of Emulsion Explosives
The commercial explosives industry produces some I.5 Million metric tons of explosives
each year in the United States, Traditionally, this has been made up of three types of
1. Nitroglycerin dynamites, which may be gelatinous, granular, or intermediate,
depending on the ratios of solid and gelled liquid components,
2. Dry blasting agents, which are essentially dry mixtures of ammonium nitrate and a
variety of fuels, including hydrocarbons and aluminum metal. ANFO, a mixture of
porous AN prills and fuel oil, is by far the most extensively used industrial explosive.
3. Slurries and Emulsions, which are gelled or emulsified aqueous solutions of
ammonium nitrate and other nitrate salts with undissolved salts, carbonaceous fuels,
and sensitizer ingredients such as finely divided aluminum and molecular explosive
ingredients such as TNT.
By common usage the term emulsion explosive is taken to mean a high-internal-phasewater-in-oil (or invert) emulsion of a concentrated solution of nitrate salts in water
emulsified into an oil base. Current developments are aimed at resolving such practical
problems as stability and prevention of crystallization, as well as attaining specific design
objectives relating to cost, rheology, and detonation parameters.
Before proceeding to a discussion of the science and technology of emulsions, we must
first digress to point out some of the pertinent features of explosives. Generally, the
explosives of commerce consist of an intimate mixture of condensed oxidizers, almost
invariably the nitrate salts of ammonia, sodium, and calcium, which are mixed with a fuel
and usually other additives. The purpose of the latter is to control rheology and to
provide the correct reactivity, physical form, and density to ensure reliable detonation.
Such mixtures are used in three physical forms for three different methods of loading into
drilled holes: as prilled solids which are poured or augured into boreholes; as pumpable
liquids which are loaded from a truck in bulk directly into the ground; and in the form of
stiff pastes or gels which are packaged into paper or plastic tubes and sold by the case.
The latter packaged explosive type is by far the smallest tonnage of the three but
represents the highest value. It is also the most technically sophisticated, as it must meet
requirements of shelf life, resistance to handling, immunity to changes in temperature,
etc. Emulsion explosives are also characterized by a number of unusual scientific
features. Their detonation capabilities and particularly, their high velocities of detonation
depend on maintaining a very Intimately mixed, all-liquid system. In practice, this
requires droplet sizes on the order of 1 micron. Since water proves to be an effective
detonation inhibitor, the desired sensitivities are achieved by controlling water levels in
the formulation. Finally, the requirements of redox stoichiometry create a situation that
can be resolved only by the use of a large volume of highly supersaturated (and therefore
metastable (and sometimes unstable)) salt solution, finely dispersed in a small volume of
hydrocarbon oil. As In most other industrial explosives, AN is the major ingredient, about
70% of the over all composition. The dispersed aqueous phase, which constitutes over
90% by weight of the liquid fraction, and generally contains other salts such as sodium
and calcium nitrates, is emulsified into 7 to 10% of oil or oil/wax phase. Additional solid
ingredients (generally under 15%) include glass or plastic microbubbles, aluminum
powder as an energetic fuel, and some quantities of the particulate salts. A variety of
other ingredients, i.e. sensitizers, may be added to perform specific functions. Stability
requirements are particularly demanding for the packaged versions of these products and
must withstand wide ranges of temperature for many months in storage and
transportation without significant crystallization, particle growth or emulsion breakdown.
All failures of the emulsion systems lead in turn to loss of the required explosive
properties. Storage time is limited to 1 year at ambient temperatures.
In 1961, Egly and Neckar  of Commercial Solvents Corp. disclosed that a water-in-oil
(W/O) emulsion of concentrated metal nitrate solutions in paraffin oil could be made by
the use of a fatty acid-based oxazoline and that this emulsion material had utility in an
explosive. The discovery does not seem to have been followed up, however, and the
next advance was made by Atlas Powder Co. [35,36], in their patents of 1966-1969,
where nitric acid wall emulsion into an oil phase to produce an explosive, albeit one of a
rather corrosive nature. In a landmark patent of 1967, Bluhm  showed that
commercially usable explosives could be made by forming a water-in-oil emulsion of
about 90% internal phase (v/v) from a hot nitrate solution, a paraffinic oil or wax, and a
number of emulsifiers, the preferred being fatty acid derivatives of sorbitol (Span or
Arlacel type emulsifiers). With the addition of some gas microbubbles to lower the
density (thereby ensuring detonability), such a system formed a very simple explosive.
The stoichiometry of the reaction between ammonium nitrate and a Hydrocarbon is:
3nNH4 NO3+ (CH2) n nCO2 + 7nH20 + 3nN2
The stoichiometric ratio requires 17 times as much ammonium nitrate by mass or about
10 times as much ammonium nitrate solution by volume as oil.
From the time of Bluhm’s invention, improvements only have been made to his original
formulation. Although such improvements are essential for the commercial acceptability
of the products they leave the basic concept unchanged.
An emulsion explosive, then, is conventionally formulated with three components that
influence the emulsion: aqueous phase, emulsifier, and oil phase. As has been
mentioned, other additives, which have no real effect on the emulsion structure, are
added to make these compositions detonable, and these will be described later.
The aqueous phase makes up some 90% or more of the formulation and conventionally
consists of a melt of ammonium nitrate, sodium nitrate, and calcium nitrate with a little
water to lower the melting point, A typical composition contains from 10 to 20% water and
is usually made up so that the composition is close to a eutectic point. For example,
most packaged explosives are made from an ammonium nitrate, sodium nitrate/water
melt of composition approximately 73/14/3.3 [4,5], although each manufacturer has a
preferred ratio. Such a melt has a crystallization point (more properly called “fudge
point”) of around 70°C and therefore must be heated before inclusion Into the emulsion, It
is one of the startling features of this system that in a properly formulated emulsion
explosive the droplets of this melt phase remain liquid down to temperatures as low or
lower than -20°C. That they can be subjected to such supercooling is attributable to the
large degree of subdivision, which ensures that the number of droplets far exceeds the
number of heterogeneous nuclei present. It is essential for the proper functioning of
emulsion explosives that these droplets remain liquid, and a great deal of research has
been devoted to means of preventing crystal growth and its, propagation through the
Not all emulsions are made from such highly supersaturated solutions. Products to be
loaded In bulk generally contain more water and even large amounts of calcium nitrate,
which lower the crystallization temperature, making manufacture and handling simpler
and sometimes lowering the detonation sensitivity of the product [40,41,42] . Some
emulsion explosives have even been formulated with no water [43,44,45] at all,
employing a eutectic mixture of metal and ammonium nitrates with urea.
Early in the evolution of emulsion explosives it was realized that the oil phase (continuous
phase) played a highly important role in stabilizing these systems. Indeed, Bluhm's early
patent  calls for the use of highly refined (highly paraffinic or naphthalenic paraffin oils
and waxes in order to make stable products, and Brockington  and Wade [39,47]
showed that the use of such refined waxes was essential to obtaining long-term stability
under a variety of conditions. A number of types of waxes have been claimed to be
effective in this system, including microcrystalline waxes [39,47], insect waxes ,
candelila , polyolefin , and paraffin . Since stability is less of a concern in bulk
delivered explosive, it has proved possible to make bulk products from less refined
materials  or even waste products. There are also some indications in the patent
literature that packaged products can be made similarly . Storage limitations are still
generally restricted to less than 24 months.
Many Japanese authors exemplify their patents with formulations containing unpurified
microcrystalline waxes . Yorke et al.  have shown recently that a wide range of
crude or partially refined petroleum products can give results as good as (or even better
than) the refined products commonly used. Petroleum products can also be replaced
totally by other oils, such as epoxidized soya bean oil .
Occasionally, the hydrocarbon oil/wax emulsions are insufficiently reactive for some
industrial applications and some researchers [56,57,58] have attempted to employ more
energetic oil phases. In particular, nitroglycerin, TNT, nitropropane, and di-nitrotoluene
have been examined. It has proved impossible to make formulations of sufficient stability
using these oils, and commercial products have not yet proved to be feasible. However,
higher performance will undoubtedly lead to higher sensitivity.
Surfactants In emulsion explosives have two roles to play. They’re primary function Is to
form and stabilize the high internal phase W/O emulsion (≈ 90% v/v Internal Phase) at
However, once formed, these systems are cooled,
supercooling the internal phase. This requires that the emulsifier also be capable of
maintaining this supermodel states which implies that the surfactant does not nucleate
the nitrate salts. Also, the surfactant must prevent those droplets that are inevitably
nucleated from crystallizing the rest of the emulsion. Many materials have been claimed
to be effective for this task and they cover an enormous range of types and hydrophilelipophile balances (HLBs).
Stability of Emulsion Explosives
Emulsions usually “fail-safe,” i.e., when stored for an excessive period of time they
become almost impossible to detonate. This is an important safety feature; however, the
manufacturer must ensure that products will still function at full performance after the
maximum time they are likely to be stored in a customer’s magazine. Stability is related
to this requirement, as described below . However, on more than one occasion,
aluminized emulsion explosives have been known to spontaneously react and either
burn, explode or detonate due to breakdown of the emulsion droplets and exposure of
aluminum to water containing concentrated oxidizer .
Because or the presence of supersaturated droplets, emulsion explosives are an
inherently metastable system. As noted above, this supersaturation may break down
completely if the emulsion is cooled to a sufficiently low temperature.
With many commercial formulations a spectacular demonstration of nucleation can result
from a sharp blow to the emulsion. The product nucleates because of the shear, it
crystallizes, and the temperature rises rapidly. The material hardens noticeably within
minutes. Emulsion explosives having large droplets are less sensitive and have larger
critical diameters than those having smaller droplets. The fuel/oxidizer reaction is slowed
by an increased diffusion length. Coalescence therefore leads to a deterioration in
detonation properties. Also, large droplets have an increased chance of containing a
heterogeneous nucleus, and therefore higher crystallization probability. It should be
realized that crystals are not necessarily confined to their original droplet size and shape
but can break through the films separating droplets.
The patent to Bluhm  is generally regarded as the first to describe all the components
together in the form of a W/O emulsion explosive as it would be considered today. The
stability was stated to be "good" with no phase separation, however, the importance of
super-saturation seems not to have been fully understood. In packages, the stability has
been found to be inadequate and improvements have been required.
Cameron and Cooper  described emulsions stabilized by an alkyd polymeric
surfactant, while Nippon Oil and Fats  describe an ethylene oxide-propylene oxide
copolymer. Wade  discovered increased stability when a blend of microcrystalline
wax and paraffin wax is used, rather than either alone. Takeda et. al.  claim high
stability for emulsions containing a high-melting-point wax which contains a high
proportion of urea non-adduct component. Yorke et al.  showed the advantages of
using a crude hydrocarbon mixture (e.g., slackwax) of a wide molecular weight
The monomeric surfactant used may have important effects on stability. Sudweeks and
Jessop  claim habit modification of any crystals formed in an emulsion containing a
C14 to C22 fatty amine or ammonium salt as an emulsifier. This effect limits the growth
and size of the crystals. The same authors  claim that cationic surfactants having
unsaturated lipophilic chains give substantially improved stability over their saturated
counterparts. Similarly others [62,63] have shown that phosphates are capable of crystal
Binet et. al.  claim increased stability in emulsions containing at least one
conventional water-in-oil emulsifier and at least one amphipathic synthetic graft, block, or
branch polymeric emulsifier. The increased stability was ascribed to the highly ordered
and stable film formed in the presence of the polymeric emulsifier and this assertion was
supported by calorimetry measurements.
Detonation Properties of Emulsion Explosives
The W/O emulsion of concentrated nitrate salt solution in oil is not, in itself, an explosive.
To It must be added gas bubbles and (optionally) metal fuels or solid nitrates in order to
produce an effective commercial explosive. The addition of metal fuels is simply to
increase the power of the explosive. For example, the addition of aluminum results in
about 100 kJ/kg of product for each 1% of aluminum incorporated. The addition of solid
nitrates is used to reduce the cost of these materials.
The presence of gas bubbles is necessary to ensure the detonability of the emulsion.
These bubbles provide a mechanism (bubble collapse, jetting, adiabatic compression),
for the conversion of the energy in the detonation shock wave to the heat energy
necessary to produce chemical reaction and, therefore, sustain the detonation. Emulsion
explosives differ from most other explosives of commerce in that they rely only on these
bubbles for their sensitivity. Other, more traditional explosives have depended on
chemical sensitizers as well. It is therefore not surprising to find that type and distribution
of these bubbles is critical in determining the detonation performance of emulsion
explosives. A review of this effect has appeared from Nippon Oils and Fats [65,66].
The traditional void material is glass microballoons, chosen for the combination of good
emulsion stability, high velocity of detonation (Vd), and resistance to static pressure
effects. Glass microballoons amount to 30% of the raw material cost of a small diameter
emulsion, and commercial introduction of a wide product range of emulsions may depend
on at least partial replacement by some other void material. A large number have been
tested: mechanically entrained gas , chemically generated gas , perlite ,
inorganic foam and expanded polystyrene. Perlite is advantageous regarding costs, but
the small-diameter products have low Vd values and limited stability. The use of perlite in
intermediate diameters would seem to be acceptable. The effect of void size on the
detonation properties of emulsions is now well studied. Small voids (<30 µm) yield
products of high detonation velocities but low sensitivity, the product behaving as
pseudohomogeneous. Large voids yield products of lower detonation velocities but high
sensitivity and are more like the classical hot spot model. Use of a large proportion of
voids over 75 µm in diameter offers the possibility of detonation cord-sensitive products
without added sensitizers.
Gas bubbles and microballoons show ideal behavior in emulsion; that is, the velocities of
detonation observed approach those predicted for thermodynamic-hydrodynamic
computer codes. However, the coarser voids, such as perlite and polystyrene, produce
highly non-ideal detonations in this type of analysis.
It is not only the size (type) of void that is important in determining the detonation
characteristics of emulsion explosives; there is also an effect of the quantity of these
voids (i.e., the density of the product). With increasing density there are fewer hot spots
per unit volume and a lower extend of reaction, which leads to a falling velocity of
detonation. In the limit, this results in failure of the detonation at high densities.
The "ideality" of non-aluminized emulsion explosives (i.e., the fact that their detonation
velocities approach those predicted by theoretical models) is one of their attractions to
the industry. These materials detonate with high velocities (i.e., very rapid reactions) and
a large proportion of their thermodynamic energy contributes to the detonation. This is
different from other commercial explosives, where much of the available energy is
produced in slow burning reactions following the detonation. In certain blasting
applications, this high velocity is an advantage producing high detonation pressures
(brisance) and shattering the rock well.
In summary, emulsions are of interest to the explosives industry because they offer the
possibility of producing all types of products with one simple system. In particular, small
diameter cap sensitive explosives can be formulated without added explosive sensitizers.
The sensitivity is a function of the degree of contact of fuel and oxidizer and of the
supersaturation, which ensures that a large amount of energy is concentrated in the liquid
phase, where reaction is rapid. This Is in contrast to slurry explosives (which consist of a
sensitizer, a continuous oxidizer solution phase, solid ammonium nitrate, and a gelling
agent), where the oxidizer is present in solid form and where chemical reaction is about
an order of magnitude slower. In emulsion explosives complete reaction can occur in
about 1µs. In slurry explosives, complete reaction usually requires a considerably longer
Because of the supersaturation, emulsions maintain their cap sensitivity almost
unchanged down to low temperatures (-20ºC or better). On the other hand, in slurries,
crystallization from the liquid component occurs with falling temperature. As a result,
there is a drop in the energy of the fast-reacting components and a decrease in
sensitivity. By adjusting mixing and formulation variables, the detonation properties of
these materials can be varied widely, further adding to their utility.
Limitations of Emulsions
Deficiencies of emulsions are as follows: Aluminized emulsions also suffer from the
same long term storage problems associated with slurries. However, due to the
instability of the emulsion itself, typically the emulsion breaks down and massive
crystallization occurs before aluminum begins to thermally react with the AN and water.
Additionally, due to the high temperature associated with ensuring high salt density, the
same self heating concerns exist with emulsions as with slurries. Finally, and most
importantly for the purposes of this project, emulsions still (by virtue of the relatively high
concentration of water (which both decreases density and reaction temperatures), suffer
from poor performance characteristics relative to the project goals. Emulsion explosives
have a detonation pressure 360% below the target goal while emulsion blasting agents
have a detonation pressure 500% below the target goal.
Development of PBX Explosives
Plastic Bonded Explosives (PBX) is a term applied to a variety of explosive materials
which are characterized by high mechanical strength (above 10,000 psi compressive
strength), good explosive properties (usually > 7800m/sec detonation velocity (Objective
# 1)), excellent chemical stability, insensitivity to handling and shock (to extremes of from
10% to 40% above basic explosives (Objective #2)), and high thermal input insensitivity
with the average autoignition temp > 250 ºC (Objective #2). These explosive mixtures
contain a large percentage of basic explosives such as RDX, HMX, HNS or PETN in
intimate mixture with a polymeric binder such as polyester, polyurethane, nylon,
polystyrene, various types of rubbers, NC, or teflon. In some instances a plasticizer such
as di-octylphthalate (DOP) or butydinitrophenylamine (BDNPA) is included in the
ingredients as well as a fuel such as Al or Fe powder for blast enhancement. Plastic
Bonded Explosives are also waterproof (Objective #3), are easily boostered (Objective
#6) with low critical diameters (Objective #7) and high pressures, are non-TNT based and
have excellent long term storage characteristics (Objective #10). However, while PBXs
are shock insensitive to some degree, they are still susceptible to a number of other
types of shock (such as projectile impact and slow cook-off) and therefore, while more
shock insensitive than TNT based explosives, are not the final solution. 
Much of the advantage stemming from the use of PBX compounds is in the simplicity of
the technique of the end item manufactured. About half of the developed PBX
compounds are used to directly cast end items such as for the lunar seismic experiments.
The first attempts to desensitize RDX were reported by Frankel and Carleton [69-73] who
made use of polymeric materials such as polyurethanes to coat explosive crystals by
means of emulsion or solution techniques. The first true PBX was developed in 1952 at
the University of California and consisted of RDX coated with polystyrene plasticized with
Lunar seismic explosives were evolved during the 1960's and early 1970's using Teflon
as the binder [75,76]
There are more than several PBX compounds developed outside of the USA or by USA
non-military organizations which are of interest and are presented here. The PBX
developed by Wright  is a molding powder prepared by mixing a water dispersion of a
binder such as a polyacrylate, a plasticizer such as paraffin oil, with a water slurry of an
explosive such as RDX and a coagulant such as ethanol. Hard, well-formed granules are
produced which contain 90-98% explosive. Subsequent pressing at 25000 psig and
49ºC, yields pellets with a compressive strength of 10000 psi. In another explosive
patented by Wright  much the same procedure is followed using, in this instance,
polyhexamethyleneadipainide as the binder and diaminotrinitrobenzene (DATB) as the
explosive . The product contains 90-98% explosive with a bulk density of 0.60.7g/cm3.
Sato  reported the development of a PBX series using PETN and a combination of
Epikote 871 (an epoxy resin) co-polymerized with diethylenetriamine in percent ratios of
70/30, 65/35 and 60/40 (explosive/binder). The compression strength of this explosive
series averages 60 kg (F)/cm2.
Vacek and Skrivanek  invented a series of PBXs using an aqueous dispersion of
poly-vinyl acetate binder, PETN as the explosive, with dibutylphthalate (DBT) as the
plasticizer in a typical wt % ratio of 36/60/4. A typical detonation rate is 5200 m/sec using
a 28 mm charge diameter with a density of 0.92g/cm3.
A self-supporting PBX series has been developed by Minekawa et. al.  which can be
fabricated in plate, strand or tape form for use in metal forming by impulsive loading. The
compound can include polyethylene as binder, a paraffinic hydrocarbon as plasticizer,
and an explosive/oxidizer combination. The development of PBX compounds using a
polyester as the binder and RDX as the explosive has been reported by Reichel .
Evans  invented a PBX series with compounds using, for example, PETN as the
explosive, a polyethacrylate rubber as the binder, and dibutylphthalate as the plasticizer
in wt % ratios of 60-85/10-40/0-10. A typical product detonates with a No 6 electric
blasting cap at a rate of 8180 m/sec.
In another PBX series, that of Butler et. al. , β-hydroxyethylacrylate is the binder,
ethylene glycol is a copolymer, benzoyl peroxide is the catalyst, while LiCIO4 is the
oxidant, and RDX or HMX is the base explosive . A typical wt % ratio is 20/13/1/9/57.
An invention of Kegler et al  has increased the pot life (before molding) of PBX
compounds containing 5-15% polyester binder by several days through the use of gelatin
microcapsules to enclose the benzoyl peroxide. The catalyst is released during the
pressure molding operation.
Frankel et. al. [86 & 87] developed a series of nitrofluoroalkyl epoxides (epoxy ether
explosives) which are heat and impact stable and are used as binders with RDX (80%)
as the explosive.
A flexible, self-supporting PBX was patented by Rothenstein  which uses fine
particulate explosive in an admixture with low density prepolymers. For example, using
hydroxyl terminated polybutadiene (HTPB) as the binder, RDX as the explosive, toluene
di-isocyanate (TDI) as a co-polymer, sym-di (2-naphthyl)-p-phenylenediamine as an
antioxidant, and polybutene as the plasticizer in a weight % ratio of 12.1/42.7/5/0.2/40,
producing a castable explosive.
Several manufacturing procedures are currently used to produce PBXs. One of these
techniques is that of casting. This procedure, at first glance, merely involves combining a
dried explosive , such as RDX, with binder constituents and curing initiators in a mixing
vessel, blending to desired homogeneity followed by casting. Unfortunately, there are
hazards associated with the drying of large quantities of explosives such as HMX or
RDX. Hence, a desensitizing procedure must be added for production scale operations.
This procedure involves coating the HMX or RDX (which is normally water wet for
storage and shipping), with the alkyl or polyester portion of the binder. The resulting
lacquer is added slowly to an aqueous slurry of the HMX (or RDX). Agitation at
approximately 250 rpm in the presence of water causes the resin to precipitate onto the
surface of the HMX (or RDX), producing an insensitive powder which may be safely
dried, handled, shipped, and stored until ready for use in the final PBX compound. The
pre-coated explosive is then combined in a mixing kettle with sufficient copolymer to
constitute the final binder compound. An accelerator (such as co-naphthenate) is added
at this point. The mixture is then stirred until homogeneous, at first under ambient
pressure, and finally in a partial vacuum to remove entrapped air. The curing agent (such
as methyl ethyl ketone peroxide) is then added. After another short mixing period (≈15
min) the explosive compound is poured into the desired molds. Vacuum casting has
been found necessary to obtain optimum density.
Plastic Bonded Explosives are used wherever high mechanical strength, high energy,
high heat insensitivity and relatively low shock sensitivity are required. Unfortunately,
there was no PBX available at the time that this research began which met the project
objectives as defined in Section 1.4. However, the high performance PBX composition
known as PBX-109 was used as a baseline PBX composition, although this composition
is considered quite sensitive and is a Class 1.1 explosive.
Deficiencies of Modern Explosives
Modern day commercial explosives, principally ANFO, slurries and emulsions, still have a
number of deficiencies as follows. First and foremost, for the purposes of this project,
commercial explosives have relatively low performance. As stated earlier, higher
performance translates to a lower amount of explosive required to perform a job and
increased safety. ANFO as well as typical slurry/emulsion explosives/blasting agents
have detonation pressures from between 350% to 775% lower than the target goal of
240 kbars ± 10%. Due to the relatively low densities (i.e. 0.82 for ANFO) and/or
presence of water, performance characteristics of these explosives are much lower than
the project goals. Table 1.3-1 compares a number of characteristics of slurry, emulsion
and ANFO explosives with H-6.
Slurry, emulsion and ANFO explosives and blasting agents have a number of other
deficiencies other than low performance [Objective #1]. Slurry and Emulsion explosives
are still somewhat sensitive and are classified as Class 1.1 explosives because they are
cap sensitive [Objective #2]. Due to the presence of water, emulsion and slurry
explosives/blasting agents do not function well below temperatures below freezing (due
to the presence of water) [Objective #7]. Also, due to the presence of water and/or
hygroscopic nature of ingredients, typical shelf lifes are less than 2 years at best and can
be as low as a few months [Objective #9]. Objectives 4 (Steam Kettle
Processability) and 5 (Less Than 24 Hour Cure) are not applicable due to entirely
different manufacturing methods. Therefore, of the 8 applicable goals, half of the goals
are not met with slurry or emulsion explosives/blasting agents or ANFO. Table 1.3-2
details Project objectives and compares Emulsion and Slurry Explosives/Blasting Agents,
ANFO and H-6 with regards to the project objectives.
Project Objectives and Approach
The project objectives were to develop an energetic material with the following
First, an explosive must perform in order to complete the designed task (i.e. break up of
rock formations). As a goal, therefore, very high performance (comparable to the
explosive H-6) was of primary importance. While the performance of H-6 is very high
(relative to typical commercial explosives) it would not be very difficult to reduce
performance (once achieved) so that insensitivity could be improved. Additionally, there
is a significant amount of data available on H-6 which could permit its use for
Secondly, the explosive should be insensitive to accidental initiation. The explosives
developed (assuming they qualified for large scale testing) were subjected to the most
difficult shock and thermal test standards known.
Third, it would be desirable for the explosive to be waterproof in order to permit blasting
in areas where water is present (i.e. limestone blasting (dead coral) in low lying levels
such as South Florida).
Fourth, in order to take advantage of surplus explosive manufacturing equipment, the
energetic material must be processable in standard TNT steam kettles. The closing of
numerous government owned explosive processing facilities in the US (and subsequent
conversion to private industry usage) has allowed enormous amounts of equipment to
become available to commercial explosives manufacturers. It was therefore a primary
goal to develop an energetic material which could be processed in existing TNT type
processing equipment and which would be self curing or would solidify once cooled (in a
manner similar to TNT). By meeting these goals, commercial energetic material
manufacturers would be more likely to manufacture the energetic material and make the
energetic material commercially available.
Fifth, In order to reduce time and cost, the explosive must be curable in less than 24
Sixth and Seventh, in order to for the explosive to be easily initiated, the energetic
material must have a low critical diameter and sufficiently shock sensitive to permit
initiation with standard boosters
Eighth, since TNT itself continues to be responsible for a high number of explosive
accidents, development of an insensitive non-TNT based energetic material (with
comparable cost and performance) would result in a significant safety improvement to the
Ninth, since most commercial explosives only have a shelf life of 1 year or less before
they either become ineffective or become very sensitive. Indeed a number of aluminized
slurry formulations have detonated on their own due to the slow reaction between water
and aluminum. Most emulsion explosives are not sufficiently stable to ensure reliable
performance after 1 year. Therefore, it was a goal of this project to develop an explosive
with a shelf life of 10-20 years.
Tenth, although, not a primary goal, in order for commercial explosive manufacturers to
find the energetic material financially attractive, it would be desirable for the explosive to
have low raw material cost with high raw material availability. Therefore, it was a goal to
develop an insensitive energetic material which could be produced for a cost not more
than 2-3 times more expensive than typical commercial explosives. However, cost
should never take priority over proper application of explosives, particularly when safety
may be affected. It is important to note that the price of the explosives is only one factor
to consider in evaluating the cost of blasting. Inexpensive explosives that do not serve
the purpose for which they are intended are no bargain. High-energy explosives may
have a higher initial price, but savings in drilling, loading, and mucking the rock may
offset this cost . Additionally, the costs associated with explosive accidents (in terms
of loss of and injury to human life, as well as monetary losses) far outweighs the
additional costs which may be associated with the production of safer explosives.
The project objectives are summarized in Table 1-3.
Summary of Project Objectives
Steam Kettle Processability (Viscosity < 2kp)
Less Than 24 Hour Cure
Boosterable with Standard Boosters
Low Critical Diameter
Ten to Twenty year Shelf Life
Low Raw Material Cost and High Raw Material Availability
The Project Approach is detailed in Figure 1.4-1 (Theoretical) and 1.4-2 (Research).
The theoretical approach for the project consisted of the following format (Figure 1.4-1).
First, a thorough literature review occurred to determine the state of the art in the field of
Insensitive High Explosives.
Second, a thorough theoretical analysis of the raw materials (Molecular Explosive,
Reactive Metal Powders, Binder and Oxidizer) occurred from predicted sensitivity (based
upon literature review and prior experience), performance (based on thermochemical
calculations), cost/availability (based upon vendor quotes), cure property (based upon
literature review and prior experience) and processing standpoints (based upon packing
Third, additional thermochemical calculations were conducted to optimize potential
Fourth, theoretical solids particle size distribution and content was calculated to optimize
processing, viscosity and solids loading.
The research approach for the project consisted of the following format (Figure 1.4-2).
First, small scale (450 gram) energetic material processing and testing (for sensitivity and
Second, once the processing, sensitivity and performance characteristics were defined
and determined acceptable, scale-up to intermediate scale (4.5 kg) mixing occurred
followed by additional performance and sensitivity testing.
Third, once the intermediate scale processing, sensitivity, and performance
characteristics were defined and determined acceptable, scale-up to large scale (23 kg)
mixing occurred followed by large scale performance and sensitivity testing.
Fourth, once the interim project objectives were achieved, then the project was
terminated. If the interim project objectives were not achieved, then energetic material
reformulation would occur as required.
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70. Ibid. Report No. 562 (1951)
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73. Ibid., Report No. 660 (1952)
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FIGURE 1.1.2-1 POST AMMONIUM NITRATE DETONATION FIRES (TEXAS CITY, TX)
FIGURE 1.1.2-2 PORT AREA AFTER AMMONIUM NITRATE DETONATION (TEXAS CITY,TX)
FIGURE 1.1.2-3 PORT AREA POST AMMONIUM NITRATE DETONATION (TEXAS CITY,TX)
FIGURE 1.1.2-4 PORT AREA POST AMMONIUM NITRATE DETONATION (TEXAS CITY, TX)
FIGURE 1.1.2-5 AERIAL VIEW OF PORT AREA/CHEMICAL PLANT FIRE (TEXAS CITY, TX)
TEMPORARY OPEN AIR MORGUE FACILITY (TEXAS CITY, TX)