Sept. 24, 1963 N. J.

BOWMAN ETAL 3,104,994

SM

?S-AF>EK&<)È 9

By

Cz ZZZZZZZZZZZZ
 3,104,994
United States Patent Office Patented Sept. 24, 1963
2
of ammonium nitrate and also the approximate volume
3,104,994 change in terms of percent.
SOLD AMMONUMNTRATE EXPLOSIVES
AND PROPELLANTS
Norman J. Bowman, Harmond, Ind., and Wayne A. Temperature 1 Wolume
Proe, Chicago, Ill., assignors to Standard Oil Com Phase change 1 - change,
percent 2
pany, Chicago, Ill., a corporation of Indiana o C. o F.
Filed June 20, 1952, Ser. No. 294,528
11. Clainas. (C. 149-19) Liquid to Solid (I)---------------------- 169.6
I to II--------- 25.2
This invention relates to a composition for the genera 10 II to III 84.2
II to IV 32.1
tion of gas, which composition can be used as an explosive IV to W- -18
or propellant. More particularly, the invention relates
to explosive compositions wherein ammonium nitrate is R. G. Early-T. M. Lowry, J. Chem. Soc. 115, i.187 (1919).
substantially the only explosive agent. Still more par 2 International Critical Tables.
ticularly, the invention relates to a shaped composition 5
It is obvious from the above that the performance char
for the generation of gas by the decomposition of a mix acteristics of an ammonium nitrate-base composition might
ture comprising essentially ammonium nitrate, oxygenated be seriously affected during storage at ordinary atmos
oxidizable material and a catalyst. Also, the invention pheric temperatures; since large volume changes occur at
relates to a novel composition usable as a binder for a 20 about 0° F. and about 90° F., which temperatures occur
shaped explosive. Further, the invention relates to meth very commonly.
ods for the preparation of said binder and said shaped ex The requirement for a solid propellant that is suitable
plosive composition. Also, the invention relates to a for military use is that it be ballistically stable after pro
method of propelling rockets or assisting in the propul longed storage at temperatures between about --165 to
sion of aircraft. -65 F. (-|-74 to -54 C.). Many binders have been
Ammonium nitrate is widely used as a component of used to form a shaped solid propellant (grain). However,
high explosives, particularly the so-called safe explosives. no successful ammonium nitrate-base grain has been de
Even though ammonium nitrate is classified as a high veloped by other workers in this art. Binders which pro
explosive, it is extremely insensitive- to ordinary heating duced a grain that resisted the formation of cracks (fis
and to shock and cannot readily be detonated by the local 30 sures) were sufficiently thermoplastic that the grain flowed
application of heat or by a blasting cap. Further, when at higher atmospheric temperatures and became de
ignited, ammonium nitrate alone does not burn uniformly formed; such a thermoplastic grain cannot be used because
and has a tendency to go out. In order to improve the its bailistic characteristics are not predictable. Other
burning quality to increase the sensitivity and to utilize binders which gave grains that were dimensionally stable
the excess free-oxygen available from the decomposition at these temperatures were unable to withstand the volume
of the ammonium nitrate, oxidizable materials, such as, :
carbon, cellulosic materials, hydrocarbons, etc. are ad change occurring during the transformation of the am
monium nitrate from one form to another; these grains
mixed with the ammonium nitrate. developed fissures both entirely internal and/or extending
World War II utilized in tremendous quantity rockets to the surface of the grain; such fissures act as burning
for ground-to-ground missiles, ship-to-shore missiles, air 40 surfaces and change the burning characteristics of the
to-ground and air-to-air missiles. These rockets com grain, thus making the ballistic performance of the rocket
prised essentially a thin-walled casing which contained or ATO unit unpredictable. These difficulties with am
a combustion chamber containing a quantity of solid pro monium nitrate have resulted in the use of double base
pellant, a nozzle through which the decomposition gases powders for military rockets and mixtures of special as
passed and created the forward thrust, stabilizing fins 45 phalts and ammonium perchlorate for ATO units.
and a war head which contained the explosive. The mili An object of this invention is the preparation of a gas
tary rockets utilized the so-called double base powders generating composition using ammonium nitrate as the
such as Ballistite as the solid propellant. Also, there was principal gas generating material. Another object is the
developed the use of rocket units to assist in the take-off preparation of a shaped explosive composition (grain)
of either heavily ladened airplanes or to overcome a short comprising essentially ammonium nitrate, an oxygenated
runway. These units are commonly known as JATO binder and a combustion catalyst, which grain is dimen
(jet assisted take-off) or ATO (assisted take-off) units.
The use of ammonium nitrate-base compositions as sionally about
stable and non-fissuring in the range between
165 and -65 F. Still another object is a gas
Solid propellants for rockets and ATO units is quite at
tractive because of the cheapness and availability of am 55 oxygenated binder and comprising
generating composition
a
ammonium nitrate, an
combustion catalyst which is
monium nitrate; because of the relatively low flame tem Suitable for use in rockets and ATO units. Yet another
perature of the decomposition of ammonium nitrate, be object is the preparation of a composition which is suit
tween about 3150° and 3900° F. (1730-2150° C.); and able for use as a binder for a mixture of ammonium ni
because the excess free-oxygen available from the decom
position permits the use of oxidizable material to improve 60 trate and a combustion catalyst. A further object of
this invention is a method for the preparation of said
the energy obtainable from the decomposition. How binder. A particular object is a method for the manu
ever, it was found that the physical characteristics of am facture of a shaped explosive composition which is suit
monium nitrate seriously interfered with the development able for use in rockets and ATO units. Still another ob
of ammonium nitrate-base solid propellants. ject is a method of propelling rockets and assisting in
Solid ammonium nitrate can exist in five different forms. the propulsion of aircraft. A further object is a com
These forms are stable within certain temperature ranges, 65
yet pass readily into the form stable at a different range position suitable for use as a firearm propellant or can
when the temperature of the solid is brought to the transi non powder.
tion temperature or a degree or two beyond the transition FIGURE 1 is a longitudinal view of an ATO unit.
temperature. Each phase change is accompanied by a 70 FIGURE 2 is a cross-sectional view of said ATO unit
change in the volume occupied by a unit weight of the taken along the line 2-2.
ammonium nitrate. There are given below data on the The above objects and other objects which will become
transition temperatures of the various known solid forms apparent in the course of the detailed description have
 3,104,994
3 A.
been achieved as follows. The explosive composition of cellulose acetate butyrate and is expressed as percent of
this invention comprises essentially: the initial material. A particularly suitable cellulose ace
(1)nitrate,
At least about 67 weight percent of ammonium tate butyrate is one which analyzes between about 25 and
31 weight percent of acetic acid and between about 31 and
(2) An effective amount of a combustion catalyst, and 35 weight percent of butyric acid. Commercial grades of
(3) Between about 18 and 32 weight percent of a binder, cellulose acetate butyrate are described in addition to acid
which binder comprises essentially content by its viscosity, when dissolved in acetone. Here
(A) Between about 20 and 50 weight percent of inafter the term “viscosity” as applied to cellulose acetate
cellulose acetate butyrate polymer which analyzes denotes the viscosity of an acetone solution containing
between about 7 and 55 weight percent of acetic 0 20 weight percent of the polymer. The preferred poly
acid and between about 16 and 61 weight percent mer of this invention has a viscosity of between about 10
lof butyric acid. and 40 centipoises.
(B) Between about 50 and 80 weight percent of a Methods of preparing the cellulose acetate butyrate
plasticizer selected from the class consisting of polymer utilized in this invention are given in U.S. Patents
mononitrodiphenyl, dinitrodiphenyl, mixtures of 5 1,800,860, 2,024,651, 2,030,883, and 2,135,979. Informa
mononitrodiphenyl and dinitrodiphenyl, mixtures tion on cellulose acetate butyrates which are available
of the foregoing with trinitrodiphenyl, mononitro commercially which are particularly suitable for use in
diphenyl oxide, dinitrodiphenyl oxide, mixtures of this invention are set out in a brochure of Tennessee
mononitrodiphenyl oxide and dinitrodiphenyl oxide Eastman Corporation, entitled "Eastman Cellulose
and mixtures of the foregoing oxides with trinitro 20 Esters,” ninth edition (1950).
diphenyl oxide, in which trinitro compound-con A binder having the proper characteristics for use in
taining mixtures there is an average of less than preparing the shaped explosive composition of this inven
about 2.5 nitro groups per molecule and essentially tion contains between about 20 and 50 weight percent of
not more than two nitro groups are present on any
benzene nucleus.
the defined polymer. Preferably, the binder contains be
tween about 27 and 35% of the defined cellulose acetate
25
butyrate.
The term "ammonium nitrate' as used in this specifica In order to obtain a plasticizer of the desired thermo
tion and in the claims is intended to mean either ordinary
commercial grade ammonium nitrate, such as, conven plastic characteristics and of the proper solvent action
on the polymer, it is necessary to use a compound(s)
tionally grained ammonium nitrate containing a small 30 selected
amount of impurities and which is then generally coated from the class consisting of mononitrodiphenyl,
with a small amount of moisture-resisting material Such dinitrodiphenyl, mixtures of mononitrodiphenyl and dini
as petrolatum or paraffin, or military grade ammonium phenyl, trodiphenyl, mixtures of the foregoing with trinitrodi
nitrate, or a mixture of minor amounts of other inorganic mononitrodiphenyl oxide, dinitrodiphenyl oxide,
nitrates and ammonium nitrate. mixtures of mononitrodiphenyl oxide and dinitrodiphenyl
Finely powdered ammonium nitrate contains about 20 35 diphenyl
oxide and mixtures of the foregoing oxides with trinitro
oxide, in which trinitro compound-containing
volume percent of void space. This void space must be
completely filled in order to obtain a shaped explosive mixtures there is an average of less than about 2.5 nitro
grain of the desired physical characteristics. When the groups per molecule and essentially not more than two
combustion catalyst is an organic material, some of the 40 nitro groups are present on any benzene nucleus.
void space is filled by the catalyst. However, when using It has been found that this plasticizer improves the
an inorganic compound as the catalyst, the binder must rigidity and the thermoplastic characteristics of the poly
not only fill the voids of the ammonium nitrate, but also mer without seriously affecting the oxygen demand of the
the voids present in the finely powdered inorganic material binder. The nitrodiphenyls and nitrodiphenyl oxides Such
catalyst. in order to avoid soot formation which leads as are obtained by the nitration of diphenyl and diphenyl
to a smoky exhaust, it is desirable to have the explosive 45 oxide are suitable plasticizers. The trinitrodiphenyls
composition approximately in stoichiometric balance with and trinitrodiphenyl oxides are not suitable plasticizers
respect to oxygen content. When using binders that have because of low compatibility with the polymer. How
a high oxygen demand, i.e., are low in bound oxygen ever, mixtures of nitrodiphenyls and nitrodiphenyl oxides
content such as hydrocarbons, it has been found that which contain an average of less than about 2.5 nitro
grains approaching the desired characteristics are badly 50 groups per molecule are suitable plasticizers for the pur
out of oxygen balance. Some lack of oxygen balance poses of this invention. This average nitro content may
due to excess of oxidizable materials is tolerable even be attained with mixtures of mononitrodiphenyl (oxide)
though the unbalanced composition has a lower thrust and trinitrodiphenyl (oxide), dinitrodiphenyl (oxide) and
than does the composition that is approximately in oxygen trinitrodiphenyl (oxide), or mixtures of all three nitro
balance. It has been discovered that by the use of oxy 55 compounds. It is preferred to use the dinitrodiphenyls
genated oxidizable materials as binders for the ammonium (oxides) and in particular the 2,4-dinitrodiphenyl oxide.
nitrate-base composition, it is possible to attain the desired The trinitro derivatives wherein all three nitro groups
physical characteristics
oxygen balance,
and also to attain approximate are present on one benzene nucleus in the molecule are
sensitive and tend to explode violently on heating to ele
The composition of matter used as the binder in the 60 wated temperatures. However, very slight amounts of
explosive composition of this invention comprises essen these isomers can be present without rendering the partic
tially two components. These components are a polymer ular nitrodiphenyl (oxide) unusable for the purposes of
and a plasticizer. The polymer imparts strength, tear this invention. Normally the trinitro derivative contain
resistance and rigidity to the binder and to the explosive ing mixtures will contain less than about 1 or 2% of the
grain. It has been discovered that a particular group in 65 single
undesired isomer which contains three nitro groups on a
benzene nucleus.
the generic material commonly known as cellulose ace
?tate butyrate possesses the necessary properties for the The binder of this invention contains between about 50
polymer. The cellulose acetate butyrate used as the and 80 weight percent of the defined nitro derivatives,
polymer in this invention is known as a partially esterified 70
and preferably between about 65 and 73 weight percent.
cellulose acetate butyrate and is described as having an To recapitulate: The composition of matter that is used
acetic acid content between about 7 and 55 weight per as a binder for the ammonium nitrate base-explosive of
cent and a butyric acid content between about 16 and this invention comprises essentially between about 20 and
61 weight percent. The term “weight percent acid' de 50 Weight percent of a defined cellulose acetate butyrate
notes the amount of acid obtained on saponification of the 5
polymer and between about 50 and 80 weight percent of
a defined plasticizer. Preferably, the binder comprises
 3,104,994
5 6
essentially between about 27 and 35 weight percent of compounds are selected from the chromate salts of the
polymer and between about 65 and 73 weight percent of class consisting of aliphatic polyamines, cycloaliphatic
plasticizer. polyamines and alicyclic secondary amines. Examples of
The binder of this invention is preferably prepared by these compounds are ethylene diamine chromate, triethyl
melting the plasticizer to a temperature below about 160 ene tetramine chromate, hexamethylene diamine chro
C. and adding to the hot plasticizer the desired amount mate, piperidine chromate and dimethyl piperazine chro
of polymer. As the plasticizer begins to decompose at mate.
temperatures above about 160° C., it is preferred to The aimount of chromium-type catalyst that must be
operate below this temperature and desirably below about tion present in the shaped explosive composition of this inven
150° C. The mixture is agitated while being maintained O is between about 1 and 8 weight percent and prefer
at the elevated temperature above the melting point of ably between about 2 and 4 weight percent.
the modifier, usually between about 100 and 150° C., It has been discovered that certain iron compounds are
and the agitation is continued until a substantially effective catalysts for the combustion of ammonium ni
homogeneous mixture has been attained. When cooled trate and ammonium nitrate-oxidizable material mixtures.
to ambient temperature the mixture is a very tough, horny 15 These catalysts are the subject matter of U.S. patent ap
material which has thermoplastic properties. The binder plications filed by Wayne A. Proell and William G. Stan
is readily converted to a viscous liquid by heating to a ley, Serial Number 273,564, filed February 26, 1952, now
temperature above about 100° C. Patent No. 2,987,389, and Serial Number 288,065, filed
A mixture of ammonium nitrate and defined binder is May 15, 1952, now Patent No. 2,955,033. All of the
quite insensitive and extremely difficult to ignite at am 20 taincombustion catalysts disclosed in these applications con
bient temperatures and pressures. An effective amount the iron cyanide radical, either ferrocyanide or ferri
of a combustion catalyst must be present in order to cb cyanide. In addition to the iron cyanide radical, these
tain a readily ignitable explosive composition with uni catalysts contain a second iron ion which may be either
form burning characteristics. ferric or ferro (us). In addition to the iron-iron cyanide
It is well known in this art that the addition of certain 25 complex, the catalyst may contain alkali metal and/or
ammonium ions. It has been found that the generic
types of organic materials will improve the sensitivity of classes of iron-iron cyanide compounds known as soluble
ammonium nitrate. Examples of materials which may Prussian blues and insoluble Prussian blues are effective
be added to improve sensitivity are nitrostarch, nitro catalysts for the purposes of this invention. It is known
cellulose and nitroglycerine. However, only small
amounts of these materials can be tolerated without mak 30 that the better soluble Prussian blues contain alkali
ing the composition too sensitive for use as a solid propel metal(s) such as potassium and sodium and/or the am
lant. Materials such as wood flour and sucrose improve monium radical, Some of the "compounds' which have
the sensitivity of ammonium nitrate-base explosives. been found to be effective are: ferro ferrocyanide, ferric
Nitrogen containing organic compounds are particularly ferrocyanide,
tassium ferric
ferro ferricyanide, ferric ferricyanide, po
ferrocyanide, sodium ferric ferrocyanide,
good for use as combustion catalysts when they do not ammonium ferric ferrocyanide, potassium soluble Prus
unduly sensitize the composition. Examples of suitable sian blue, sodium soluble Prussian blue and ammonium
?materials are urea, nitroguanidine, guanidine nitrate and sodium soluble Prussian blue.
mononitrate naphthalene. The element sulfur is an effec These applications show that the so-called insoluble
tive sensitizer for the ignition of ammonium nitrate. A
particularly effective catalyst for the ignition of ammoni 40 Prussian blues, either the chemical compound ferric fer
rocyanide, or the commonly known insoluble Prussian
um nitrate-oxidizable material mixtures is the element blue, are more effective catalysts at high pressure opera
carbon when present in amounts of 6 weight percent or tion than are the soluble Prussian blues. Thus when op
more. The amount of “organic combustion catalyst” erating the combustion chamber containing the solid pro
needed to render the composition readily ignitable and to 45 pellant at pressures between about 500 and 2000 p.s.i.a
produce a uniform rate of combustion varies with the higher burning rate, inches per second, is obtainable when
particular type of catalyst material added. While at least using a given composition containing insoluble Prussian
an effective amount must be present, it is preferred to keep blue
the amount of organic combustion catalyst at a minimum Same ascomposition
the catalyst than is obtainable when using the
using soluble Prussian blue as the cat
in order to obtain a grain of proper balance with regard 50 alyst. The insoluble Prussian blue containing explosive
to oxygen stoichiometry and to strength.
The most commonly used method for improving the compositions are difficult to ignite at atmospheric pres
sensitivity of ammonium nitrate-base explosives is to add Sures
about
when the amount of catalyst present is less than
6 weight percent. However, these compositions ig
a chromium containing combustion catalyst. The chromi
um containing combustion catalysts are ammonium 55 nite readily when an elevated pressure is imposed on the
chromate, ammonium polychromate, alkali-metal chro combustion Initing means.
chamber prior to the application of the ig
mate, alkali-metal polychromate, chromic oxide, chromic An application, Serial Number 288,549, fied May 17,
nitrate and copper chromite. The preferred commercial
catalyst is ammonium dichromate. The chromium-type disclosesnowthatPatent
1952, No. 3,028,273, by Wayne A. Proell,
ammoniated insoluble Prussian blue is an
catalysts are extremely effective but have the disadvan 60 effective catalyst for the combustion of ammonium nitrate
tage of being expensive and of frequently being virtually or annonium nitrate-oxidizable material mixtures. The
unobtainable; furthermore, the chromates are relatively amphoniated insoluble Prussian blue catalyst possesses the
hazardous to handle without the use of special precau ignition characteristics of the soluble Prussian blue cata
tions. A more serious disadvantage for military use is lyst and the burning rate characteristics of the insoluble
the fact that on prolonged storage at somewhat elevated 65 Prussian blue catalyst. When used in the mixture in
temperatures the chromates tend to react with the oxidiz amounts of about 2 to 4%, the ammoniated insoluble
able material in the composition to give chromate salts Prussian blue catalyzed mixture is hard to ignite and does
which are not as effective catalytically as ammonium di not sustain combustion in an inert atmosphere. The am
chromate. moniated insoluble Prussian blue catalyst is produced by
In addition to the above described inorganic chromium exposing an insoluble Prussian blue to the action of am.
70
type catalyst, it has been found that certain organo-chro monia gas. The temperature of the reaction zone con
mium compounds are effective as catalysts. These com taining the insoluble Prussian blue and ammonia gas in
pounds are disclosed in U.S. patent application Serial creases rapidly until a temperature of about 60° C. is
Number 279,968, filed April 1, 1952, now Patent No. reached; as the temperature increases, the rate of increase
2,997,377, by Wayne A. Proell. These organo-chromium, 75 decreases until at about 60° C. a plateau is reached. As

-
 3,104,994
7 8
measured by temperature increase, the interaction of ann The explosive composition of this invention can be pre
monia and the insoluble Prussian blue is believed to Sub pared by several methods. A preferred procedure is set
stantially stop when the temperature of the reaction Zone out below. The binder is heated until it has become a
reaches the plateau of about 60° C. The ammoniated in viscous fluid at a temperature on the order of 100 to
soluble Prussian blue has a strong odor of ammonia after 120 C. The desired annount of ammonium nitrate in
being cooled to room temperature. An ammoniated in a finely powdered condition is admixed with the desired
soluble Prussian blue of catalytic activity about equal to amount of catalyst also in a finely powdered condition;
the odorous material which does not possess any appre this mixing is preferably carried out at ambient tempera
ciable ammonia odor can be obtained by maintaining the tures and precautions are taken to prevent the ammonium
odorous material at a temperature of about 70° C. for O nitrate reaching a temperature approaching the melting
several hours. The ammoniation of the insoluble Prus point due to the friction of the mixing. The ammonium
sian blue does not change the physical appearance of the nitrate-catalyst mixture is slowly added to the fluid binder
material and is noticeable principally in that the catalytic while agitating the materials. The temperature of the
activity of the insoluble Prussian blue, particularly at low mixture is preferably maintained below about 120° C. in
operating pressures, is markedly improved. By this treat order to minimize the possibilities of heat ignition of the
ment various catalytically active grades of insolubie Prus composition. The materials are mixed until a smooth
sian blue can be converted to materials having about equal homogeneous paste has been obtained. This paste may
catalytic activity, i.e., the normal variation in catalytic ac be permitted to cool to ambient temperatures and then
tivity of Prussian blue obtained from different manufac broken up into irregular pieces for uses such as blasting
turers can be eliminated by this ammoniation procedure. powder. Preferably, the pasty mass is formed into shapes
The term "ammoniated insoluble Prussian blue' is in of a configuration suitable for solid propeliant purposes.
tended to include both the ammonia-odorous material The configurations are commonly called "grains.' The
and the substantially odor-free material. forming may be by introducing the pasty mass into Suit
An application, Serial Number 287,623, filed May 13, able molds, either manually or mechanically by means
1952, now Patent No. 3,044,912, by Wayne A. Proell, 25 of an injection molding technique, or preferably by ex
discloses that alkali metal-iron cyanide and ammonium trusion. The composition of this invention flows fairly
iron cyanide are effective catalysts for sensitizing the ig readily at temperatures above about 110° C. and becomes
nition and combustion of ammonium nitrate-base explo dimensionally stabie at temperatures below about 90° C.
sives. Particularly effective are potassium ferricyanide This
and ammonium ferricyanide. These “iron cyanide cata grain characteristic because it
simplifies the problem of forming the
eliminates the neecssity for accelerated
lysts are not as effective when used in compositions con cooling of the mold or the extruded grain. The composi
taining oxygenated oxidizable materials as are the iron tion of the explosive of this invention has a very large
iron cyanide complexes, the soluble Prussian blues, the advantage over conventional solid propellant composi
insoluble Prussian
Prussian blues.
blues and the ammoniated insoluble tions. It has been found that defective grains can be re
35 worked alone or in admixture with fresh materials to
When using any one or a mixture of the iron-type cat produce satisfactory grains. The reworkability of "re
alysts defined above, between about 1 and 8 Weight per
gent of catalyst is present in the explosive composition. jects' results in a substantial saving over conventional
grains where rejects cannot be reworked.
Preferably, between about 2 and 4 Weight percent of cat It has been discovered that the extrudibility of the com
alyst is used. 40 position of this invention can be greatly improved with
The iron-type catalysts are preferred for use in the out adversely affecting the characteristics of the shaped
composition of this invention because of their low cost
and ready availability. Further, they do not appreciably composition. to extrude a
It has been found that the pressure needed
tubular grain having an outside diameter
increase the heat sensitivity of the ammonium nitrate so
that preparation of the shaped grain at temperatures ap 45 to about 1000 p.s.i. bydecreased
of 0.25 inch could be from about 2000 p.s.i.
adding between about 0.2 to 1
proaching the melting point of ammonium nitrate can be
used. Particularly advantageous is the fact that at the weight percent of an alcohol, such as, heptanol, octanol,
nonanol, steryl, etc.
normal operating pressures of rocket motors and ATO The drawings show a particular application of this in
units the insoluble Prussian blues and ammoniated in vention to an assisted take-off unit. The ATO unit ilius
soluble Prussian blues give higher burning rates than do 50
the other iron-type catalysts and the chromium-type cata trated craft;
is designed to be hung under the wing of an air
normally at least two units, i.e., one under each
lysts. Still another advantage for the iron-type catalyst wing, will be used. In FIGURE 1, the body of the unit
is the fact that the residue of the iron-type catalyst is a
fine black powder producing substantially no smokiness isonemade up of a tubular member 1 which is closed at
in the combustion gases whereas the combustion residue 55 end. endMember and which is provided with threads at the open
2 is provided with two loops, 22 and
of the chromium-type catalyst is a light, fluffy material 33. These loops are used to hang the unit from a car
which imparts smokiness to the combustion gases. rier, not shown, which is attached to the wing of the
It is to be understood that the catalyst consumes some aircraft. This carrier makes it possible to jettison the
of the excess oxygen produced in the decomposition of unit
the ammonium nitrate and this consumption of oxygen 60 i4 is after take-off. A somewhat funnel shaped member
attached to member 11 by engagement of the threads
must be considered in determining the total oxygen de at the large open end of member 4 with the threads on
mand of the explosive composition. member Ai. Member 4 is provided with a nozzle 16
The explosive composition of this invention comprises through which the decomposition products pass. The
essentially ammonium nitrate, a binder and a combustion
catalyst. The ammonium nitrate is present in an amount 65 tained inside of16thedetermines
size of nozzle in part the pressure main
chamber formed by members 2 and
of at least about 67 weight percent. An effective amount 4.
of combustion catalyst must be present and when using The solid propellant fills the cylindrical portion of mem
either a chromium-type catalyst or an iron-type catalyst, ber S. The solid propellant in this illustration consists
between about 1 and 8 weight percent, preferably about of seven tubular grains, 7, 8, 9, 20, 21, 22 and 23;
2 to 4 weight percent of catalyst is present in the explo 70 each having an O.E.D. of about 3 inches and having a cen
sive composition. The amount of binder present in the traily located cylindrical opening 1 inch in diameter, the
explosive composition is between about 18 and 32 weight full length of the grain; the grains are approximately 30
percent; preferably, the amount of binder should be ad inches long. The grains used herein consist essentially
justed to give a composition that is approximately stoi of 2% of ammoniated insoluble Prussian blue catalyst,
chiometrically balanced with respect to oxygen. 75 24% of binder and 74% of ammonium nitrate.

H
 3,104,994
the hexagonal grain is dependent on the gas evolution position was prepared and maintained 2
rate desired, at a temperature
of 120° C.; by the use of an oven
The following information is presented to illustrate the to 120° C. The required amount of material the mold was heated
preparation of the binder composition and the shaped aily was manu
explosive composition; the effectiveness of the explosive placed into the mold and tamped into place with a
composition for gas generation; and the resistance of the wooden paddle. A steel disc 2.75 inches in diameter was
shaped explosive composition to fissuring when subjected then inserted into the open end of the mold and by means
of a hydraulic piston, about 100 lbs. pressure was ap
to temperatures over the range of about -100' F. to plied to the disc in order to compact the explosive ma
--170° F. terial. The mold and contents were allowed to cool
All of the test grains presented herein were made with gradually to about 50 C.; at this temperature the grain
a binder that had been prepared as follows: was removed from the mold. The grain was permitted
The polymer was a commercial cellulose acetate bu to cool gradually to room temperature and was then ma
tyrate purchased from Tennessee Eastman and listed as chined to a 2.5 inch outside diameter and was sawed into
CAB 272-20. This cellulose acetate butyrate analyzed 4 inch lengths.
between 28 and 29 weight percent of acetic acid and 5 For burning rate tests, grains about 6 inches long and
between about 32 and 34 weight percent of butyric acid; 0.25 inch in diameter were prepared by extrusion. A
the viscosity of the standard acetone solution was be laboratory extrusion device was prepared. A chamber
tween 15 and 35 centipoises at 25 C. for the explosive was adapted to be maintained at a tem
The ammonium nitrate used was technical grade and perature of betweeen 100 and 110° C. A hydraulic piston
had a particle size-"Rotap' analysis-as follows: 20 was used to force the explosive from the chamber through
Mesh size: Wt, percent retained an 0.25 inch die to give a grain of the proper diameter.
F35 --------------------------------- Trace The hydraulic piston could develop pressures up to 2000
35-60 -------------------------------- 5 p.s. i. it was found that by using this device strands 30
60-80 -------------------------------- 7 25 inches long could be prepared readily.
80-120 ------------------------------- 16 The burning rates in inches per second of various com
120-200 ------------------------------ 28 positions were determined at elevated pressures by the
200-325 ------------------------------ 19 use of a Crawford bomb. This device permits measuring
325 -------------------------------- 8 the burning rate of a strand of material at a constant
Dust --------------------------------- 17 pressure in the combustion chamber. The bomb is
The catalyst was finely pulverized in a Mikro pulverizer 30 brought to the desired pressure by the use of cylinder ni
trogen and the strand is ignited by means of a hot wire.
in order to permit more uniform distribution with the Duplicate runs were made in order to determine the re
ammonium nitrate.
producibility of the burning rates. Although there is an
The explosive composition was prepared in the follow appreciable
ing sequence of steps. The desired amount of plasticizer sure, normally change in burning rate with increase in pres
was placed in an agitated vessel and heated to 150° C. burning rates are reported at 1000 p.s.i.
The desired amount of polymer was added to the vessel sure operating pressure since this is about the operating pres
of ATO units.
and the materials maintained at a temperature of about The resistance of the particular composition to fissur
150 C. until a homogeneous viscous mass had been ob
tained. (The binder as prepared above was quite thermo 40 ing on temperature change was determined by a labora
plastic in nature and could be cooled to room tempera tory method. No standard test has as yet been estab
lished by testing laboratories and the test described below
ture to give a very tough, horny solid and then recon
verted into a viscous fluid by heating to an elevated tem awasgood
perature.)
developed by the applicants and is believed to be
indication of the “cycling resistance' of the par
The molten binder was cooled to 120° C. and then a ticular composition.
mixture of the required amounts of ammonium nitrate dersA of preliminary screening procedure utilized solid cylin
1 inch diameter and 1.5 inch length. The grain
and catalyst were added to the container. The contents
of the vessel were stirred while the temperature was main drying was placed in a glass bottle containing a small amount of
tained between about 110° and 120° C. until a uniformly of wateragent; the drying agent prevents the condensation
on the grain at Dry ice temperatures. This bot
mixed pasty mass had been obtained. This pasty mass tle was enclosed in a second glass bottle. The glass-en
was cooled to about 100° C. and then shaped into the closed grain was placed in a thermostatically controlled
desired configurations by various methods. The compo oven and
sition described above was somewhat plastic at a tem of 70° C.maintained for 4 hours at an oven temperature
(--158. F.). The glass-enclosed grain was
perature of about 100° C. (212° F.) but quickly became
rigid attemperatures below 90° C. and was quite dimen 55 then removed and held at ambient temperature about
25 C. for 1 hour. Then the glass-enclosed grain was
sionally stable at 85°C. (183°F.)
Cylinders of about 1 inch diameter and about 1.5 inches buried in Dry Ice for 3 hours; Dry Ice temperature is
long were prepared by the use of a hand press. The re -80 C. (-112 F.). The glass-enclosed grain was re
quired amount of material to make a dense cylinder was moved and allowed to come to an ambient temperature;
placed into a steel mold having a 1 inch inside diameter 60 the grain was removed from the glass bottles and in
and about 50 pounds of pressure was applied on the ma spected for cracks on the surface. (It has been noted that
terial through a close-fitting plunger. The cylinders pre grains fail by cracks that appear on the surface of the
pared in this Way Were dense and had a smooth, hard grain. Failure by internal fissuring has not occurred in
Surface. These cylinders were quite strong and could the grain configurations tested herein.)
stand a considerable amount of rough treatment. The grain was cycled to failure or for eight cycles,
Large size hollow grains were prepared for use in a whichever occurred first. Cycling tests indicate that pas
miniature rocket motor. These grains as molded were sage of eight cycles is a sufficient indication that the grain
8 inches long, 2.75 inches in diameter and had a 1 inch will cycle indefinitely.
longitudinal coaxial perforation. The 2.75 inch grain was The large perforated grains were tested as described
machined to an outside diameter of 2.5 inches for use above except that instead of using glass bottles the grain
in the rocket motor. The composition machined readily was protected by the use of a polyethylene bag. For the
on an ordinary lathe to give a grain of a smooth, very large grain it appears that successful completion of eight
hard Surface. This large perforated grain was prepared cycles indicates satisfactory resistance to fissuring upon
by the use of a steel mold which was provided with a tennperature change. it has been found that grains
1 inch steel core. The desired amount of explosive com 75 which successfully pass eight cycles on the 1 inch cylin
 3,104,994
9 O
Each grain has the aniular area at each end inhibited When using about 4% or more of the iron-type catalyst,
against burning by a coating of asphalt in order that the grain will ignite at relatively low pressures and no
the burning may take place on the cylindrical surfaces special precautions are necessary to maintain elevated
only. For some uses it is desirable to have a grain which pressure in the chamber until ignition occurs, as shown
burns cigarette fashion in which case the outer surface above. In this case, the igniter may be introduced into
and one end of the grain will be inhibited to prevent com the combustion chamber by a means attached to the coni
bustion. The inhibiting means may be asphalt, cellulose cal portion of member 14 (this procedure is convention
acetate, ethyl cellulose, acrylic plastics, etc. ally used and is illustrated in U.S. 2,479,828) and no
Although a tubular grain is illustrated herein, the in closure is placed on nozzle É6.
vention is not limited to such a grain. Any particula.T O The conventional placement of the igniter may be used
shape may be utilized. Examples of other shapes are with the lower catalyst consent grains. However, it is
cylinder, cruciform, triform, hexaform, octaform and necessary to use a much heavier powder charge in the
slab. In the case of perforated grains, the perforation igniter or, preferably, the nozzle is provided with a rup
may be circular or star-shaped with various numbers of ture disc, which is set to blow out at about 500 p.s.i.
points in the star. Furthermore, a single cylindrical grain 5 Other methods of igniting the grain can be readily devised.
having one or more longitudinal perforations may be While the invention has been illustrated by means of
utilized in some cases, instead of the multigrain unit an assisted take-off operation, it must be understood that
shown. the solid propellant of this invention can also be used for
The grains are held in longitudinal position and pre other purposes. Some of these are air-to-air missiles,
vented from sliding back and forth in the combustion 20 ground-to-ground missiles, blasting powder, etc. An im
chamber by means of a wire grid 26. Wire grid 26 consists portant use of the invention lies in the production of
of a ring cut to fit the threads of member 14 and provided gases at elevated pressures in a stationary or a portable
with a grid work of metal wires that will resist the high System; discontinuous operation is readily obtained when
temperature existing in the combustion chamber. using about 2% of catalyst as the composition can be
On one side of the conical portion of member 4 there 25 extinguished readily by merely depressuring the combus
is provided for the combustion chamber a safety venting tion chamber.
means 23. Venting means 23 comprises a tubular mem An extremely important use of the composition of this
ber fastened to member 14, which tubular member has invention lies in the field of propellent powder for small
full access to the combustion chamber and is provided arms ammunition, artillery powder and so-called cannon
with a rupture disc, not shown. The rupture disc is of powder. Small arms ammunition is intended to include
such construction that excess pressure in the combustion cartridges for pistols and rifles and shells for shotguns.
chamber will blow out the disc, whereby the pressure in Artillery ammunition is intended to include the self
the combustion chamber will be held below the point of contained ammunition, i.e., a shell wherein the projectile
serious damage to the unit. and the casing that contains the powder and igniter are
An igniter means is positioned within member 4 so in one piece, much like a rifle cartridge. For very large
as to close off the nozzle 16. The igniter means con caliber, artillery pieces such as 120 mm. antiaircraft guns
sists of a container 35 filled with black powder, or some and 6 inch or greater naval guns, separate ammunition is
other easily ignited material, which can produce a large used, i.e., the projectile and the propelling powder are
volume of gases at elevated pressure. A squib 32 for 40 Separate. Usually the powder is contained in special
igniting the powder, is attached to the container 3 in cloth bags.
communication with the powder contained therein. Elec One of the most serious problems in artillery weapons
trical wires 33 connect a wire in the squib to the elec is the extremely rapid wear of the bore, particularly when
trical system of the aircraft and a switch therein (the con firing is at a continuous high rate. The commonly used
nections to the aircraft are not shown). propellant, ballistite, has a flame temperature of about
The ATO unit is assembled as follows: The grains are 45 5900 F., which temperature softens the barrel and per
inserted into member 1. Venting means 28 are fastened mits the projectile to erode away the rifling quite rapidly.
to member 4. Igniter 31 is inserted through the large Not only is the composition of this invention much
open end and fitted so as to close the nozzle, the wires 33 cheaper than ballistite, but also the much lower flame
having first been passed through the nozzle 16. The wire 50 temperature of about 3900 F. permits a much longer
grid 26 is screwed into the large open end of member 14. useful life of the rifled barrel. Another desirable fea
The assembled nozzle portion is then securely screwed ture of this composition is that it is virtually smokeless.
onto member 25. The propellant for use in small arms is normally used
The assembled unit is then attached to the wing of the in the form of short, solid thread-like filaments varying
aircraft by loops 2 and 3; wires 33 are connected to the in length from about 0.1 to 0.2 inch. These grains are
electrical operating assembly in the aircraft. When the 55 obtained by forcing the pasty powder through a multiple
pilot desires to obtain the assisted take-off, he throws the hole die to form filaments which may be between about
switch which causes the current to pass through wire 33 1 and 5 mm. in diameter. These filaments are chilled
and to heat up the firing wire in squib 32, which in turn by an air blast in order to form long threads of pro
ignites the powder in the container 3. 60
pellant. The threads are broken into short lengths and
The container is of sufficient strength to withstand the graded by a screening operation. The diameter of the
initial pressure generated by the gases from the powder. filament-like grain controls the gas evolution rate when
The hot gases raise the pressure in the combustion cham the grain is ignited. For some uses instead of a solid
ber high enough to permit the grain to ignite. The com thread or spaghetti grain, a perforated macaroni-type
bustion of the grain causes the pressure in the chamber grain may be used. This macaroni-type grain is par
to rise to a point which cannot be resisted by container ticularly useful for smaller caliber artillery ammunition.
31. The container disintegrates and the pieces are dis For separate ammunition use it has been found that
charged through nozzle 6. The total time from throw grains which are hexagonal in external outline and are
ing the Switch to full operation of the unit is on the order provided with longitudinal perforations are preferable
of less than 0.5 second. because the hexagonal shape permits the formation of
As the gases pass out of the nozzle the reaction acts on 70
the aircraft and adds its thrust to assist the aircraft's large multiple grains of a honeycomb structure, which
propeller; a marked increase in forward speed results and grains can be readily fitted into a cloth bag of the required
permits the aircraft to take off in a shorter space of time diameter for the particular gun. These perforated hexag
or it permits lifting a load heavier than could be airborne onal grains may be as much as 1 or 2 inches in diameter
by the use of the propellers alone. and several inches long. The number of perforations in
 3,104,994
3 4.
der test also pass eight cycles on the large perforated about 20 and 50 weight percent of cellulose acetate
grain test. butyrate polymer which analyzes between about 7 and
The grains that passed the cycling test were tested for 55 weight percent of acetic acid and between about 16
internal fissuring by burning at ambient temperature and and 61 weight percent of butyric acid and (B) between
pressure. Smooth burning indicates no fissures are pres about 50 and 80 weight percent of a plasticizer selected
ent as fissures cause uneven burning, i.e., sudden in from the class consisting of mononitrodiphenyl, dinitrodi
creases in gas evolution result when a fissure is reached. phenyl, mixtures of mononitrodiphenyl and dinitrodi
In order to simulate larger scale operation, a miniature phenyl, mixtures of the foregoing with trinitrodiphenyl,
rocket motor was constructed. This motor consisted es mononitrodiphenyl oxide, dinitrodiphenyl oxide, mixtures
sentially of a cylinder closed at one end and threaded at 0. of mononitrodiphenyl oxide and dinitrodiphenyl oxide
the open end. The straight side of the cylinder was and mixtures of the foregoing oxides with trinitrodiphenyl
about 8 inches long and the cylinder had an internal di oxide, in which trinitro compound-containing mixtures
ameter of about 3inches. A funnel-shaped portion pro there is an average of less than about 2.5 nitro groups per
vided with an opening for the attachment of a nozzle molecule and essentially not more than two nitro groups
and provided with threads at the larger end was threaded 15 are present on any benzene nucleus.
onto the cylindrical casing to complete the combustion 2. The composition of claim 1 wherein said combustion
chamber of the motor. Various sized orifices were pro catalyst is ammonium dichromate.
3. The composition of claim 1 wherein said combustion
vided in order to permit the operation of the motor at
different combustion chamber pressures. These orifices catalystpercent is present in an amount between about 1 and 8
varied from 0.17 to 0.24 inch in diameter. By varying 20 weight and said catalyst consists of at least one
the orifice size, the combustion chamber pressure could member of the class consisting of iron-iron cyanide com
be varied from about 700 to about 2000 p.si. plexes, soluble Prussian blue, insoluble Prussian blue, am
In order to reduce the amount of explosive material moniated insoluble Prussian blue, ammonium iron cyanide
needed per motor test, a perforated cylindrical aluminum and alkali-metal iron cyanide and mixtures thereof.
4. The composition of claim 1 wherein said catalyst is
slug, 2.5 inches in diameter and 4 inches long, was used 25 ammoniated
to take up about half the longitudinal volume of the insoluble Prussian blue and wherein said
motor. Thus in operation the motor contained the slug catalyst is present in an amount between about 1 and 8
and a 2.5 inch diameter perforated grain 4 inches long. weight percent.
The grain was ignited by a black powder mixture, analyzes 5. The composition of claim 1 wherein said polymer
which mixture was in turn ignited by means of an elec 30 acetic between about 25 and 31 weight percent of .
acid
trical squib. It was found that satisfactory ignition could of butyric acid. and between about 31 and 35 weight percent
be obtained by using 25 g. of the following mixture: 6. The composition of claim 1 wherein said plasticizer
sparkler powder, 10 g; FFG gun powder, 7.5 g.; and
FFFG powder, 7.5 g. This mixture was placed at the is dinitrodiphenyl.
nozzle end of the funnel-shaped member and was held in 35 7. An explosive composition which comprises essentially
place by means of a paper disc pressed firmly against (1) at least about 67 weight percent of ammonium nitrate,
the sloping sides of the member. The motor was as (2) between about 2 and 4 weight percent of a combustion
sembled by inserting into the casing first the aluminum cyanidecatalyst selected from the class consisting of iron-iron
slug and then the grain to be tested. The test grain was 40 ian blue,complexes, soluble Prussian blue, insoluble Prus
ammoniated insoluble Prussian blue, ammonium
inhibited on both annular ends by coating the annular iron cyanide, alkali-metal iron cyanide and mixtures there
area with asphalt. This inhibiting of the annuli results
in the burning of the cylindrical surfaces only. The of, and (3) between about 18 and 32 weight percent of a
nozzle end complete with powder igniter was then binder, which binder comprises essentially (A) between
screwed to the casing. The electrical squib was then in about 27 and 35 weight percent of cellulose acetate buty
serted through the nozzle opening until it contacted the 45 rate polymer which analyzes between about 25 and 31
powder mixture. This method of arming the motor is weight percent of acetic acid and between about 31 and
35 weight percent of butyric acid and (B) between about
particularly desirable because the motor is essentially 65 and 73 weight percent of a plasticizer selected from
inert until a few seconds before the test run is fired. It
has been found that this method of ignition gives ignition 50 the class consisting of mononitrodiphenyl, dinitrodiphenyl,
mixtures of mononitrodiphenyl and dinitrodiphenyl, mix
delays between about 100 and 500 milliseconds. tures of the foregoing with trinitrodiphenyl, mononitrodi
Grain. I phenyl oxide, dinitrodiphenyl oxide, mixtures of mono
The binder for this grain consisted of 31% of CAB nitrodiphenyl oxide and dinitrodiphenyl oxide and mix
272-20 and 69% of 2,4-dinitrodiphenyl oxide. The grain tures of the foregoing oxides with trinitrodiphenyl oxide,
consisted of binder, 21.5%; ammonium nitrate, 74.5%; in which trinitro compound-containing mixtures there is an
magnesium nitrate, 2%; and ammonium dichromate cat and average of less than about 2.5 nitro groups per molecule
alyst, 2%. This grain successfully passed 8 cycles in essentially not more than two nitro groups are present
the 1 inch cylinder test and the cycled grain burned on any benzene nucleus.
smoothly showing that no internal fissuring had occurred. 60 8. The composition of claim 7 wherein said plasticizer
Grain II
is dinitrodiphenyl oxide.
9. The composition of claim 7 wherein said catalyst is
This grain was identical with Grain I except that the ammoniated insoluble Prussian blue.
catalyst was a soluble Prussian blue. This grain success 10. The composition of claim 7 wherein said composi
fully passed 8 cycles in both the 1 inch cylinder test and tion is about stoichiometrically balanced with respect to
the large grain test. The burning rate in the Crawford 65 oxygen.
Bomb at 1000 p.si. was 0.115 inch per second. The cal 11. The composition of claim 7 wherein said plasticizer
culated specific impulse for this grain at a chamber pres is 2,4-dinitrodiphenyl oxide.
sure of about 1000 p.s. i. was approximately 200 seconds.
We claim: - References Cited in the file of this patent -
1. An explosive composition which comprises essential 70 UNITED STATES PATENTS
ly (1) at least about 67 weight percent of ammonium 2,434,872 Taylor --------------- Jan. 20, 1948
nitrate, (2) an effective amount of a combustion catalyst, 2,568,080 McGahey ------------ - Sept. 18, 1951
and (3) between about 18 and 32 weight percent of a 2,592,623 Turnbull -------------- Apr. 15, 1952
binder, which binder comprises essentially (A) between