US Patent 2602026: Ammonium nitrate explosive

UNTED STATES PATENT OFFICE

2,602,026
AM_ONUVl NITIATE EXPLOSIVE
James A. Fart, Tamaqua, Pa., assignor fo Atlas
Fowder Company, Wilmington, Del.,  corpo-
•  ration of Delawre
...... No Drawing. Application February 26, 1948,
Serial No. 11,330
4 Claires. (CI. 52--11)
1
Thi application relates fo explosive composi-
tions.
An object of the invention is the provision of
ammonium nitrate explosive compositions of
rates or velocities of detonation of improved sta- 5
bility.
• Another object of the invention is the provision
of ammonium nitrate explosives of decreased set-
ring tendency.
A further object of the invention is the pro- 10
vision of ammonium nitrate explosives resistant
fo alteration by temperature changes.
Other objects of the invention will be apparent
from the following description.
For. many years ammonium nitrate has been 15
employed as the principal power producing ingre-
dient of many commercial explosives. Since by
itself ammonium nitrate is hot ordinarily con-
sidered suiïicientiy sensitive for explosive pur-
poses, sensitizing ingredients are applied fo 20
ammonium nitrate in the production of practical
explosives. A common and advantageous class
of sensitizers is that of the explosive liquid nitric
esters, of which nitroglycerine alone, or mixed
with nitro sugars or nitroglycols, is the most coin- 25
mon example.
The velocity of detonation of ammonium
nitrate explosives may be varied to a considerable
extent by alteration in the grain size of the
ammonium nitrate employed. To obtain some 30
useful velocities, particularly in the lower ranges,
ammonium nitrate of relatively large grain size
is employed.
Coarse grained ammonium nitrate explosives
sensitized with explosive liquid nitric esters have, 35
however, in the past been subject fo ai least three
rather serious disadvantages:
1. They have tended fo set on standing into
hard masses which become quite insensitive and
diflicult to handle; 40
2. The have tended to fise considerably in
detonation velocity on being subjected to fluctu-
ating summer temperatures; and
3. _They bave sometimes tended fo show in-
creased velocity when detonated under confine-
ment as compared with their velocity when deto-
nated in the open.
Since explosives are ordinarily employed under
conditions of connement and are usually stored
under outdoor temperature conditions, these 0
velocity jump phenomena bave been particularly
objectionable.
If bas been found in accordance with the pres-
ent invention that coarse grained ammonium
nitrate sensitized with explosive liquid nitric ester
produces explosives of highly stable detonation
velocity characteristics and of much decreased
setting tendency when potassium nitrate is
cluded in solid solution throughout the ammo-
nium nitrate grain. With granular ammonium

2
nitrate explosives of this type, the velocity jump
on comîuement is usually greatiy minimized, and
the velocity change on temperature fluctuation is
usually practically eliminated.
Granular ammonium nitrate for explosive use
is generally prepared by evaporating solutions of
ammonium nitrate nearly fo dryness and then
cooling the molten mass under agitation, as in a
graining kettie or a continuous crystallizer. As
the ammonium nitrate cools if crystallizes and
gives off heat of crystallization which evaporates
the remaining water. The grain size and hard-
ness obtained is controlled by the amount of
evaporation prior to crystallizati0n, and also by
the addition of small quantifies of grain modify-
ing salts, such as ammonium chloride and ammo-
nium sulphate. Grain modifying salts are
usually added either in the evaporating equip-
ment or fo the graining equipment prior to the
addition of the molten ammonium nitrate.
While ammonium nitrate for explosive use is
also sometimes produced by cracking castings, the
stability improvements elIected by the present
invention are chiefly noted with material, the
grains of which are produced directly from a
melt.
The potassium nitrate employed in accordance
with the present invention may be added to the
ammonium nitrate in any manner which distrib-
utes it in complete solution. For example if may
be added directly fo the molten ammonium
nitrate, or it may be added to the crystallizing
equipment prior fo introduction of the ammo-
nium nitrate therein.
Also since ammonium nitrate solutions are
usually formed by neutralizing an ammonia solu-
tion with nitric acid, the potassium nitrate
ammonium nitrate mixture may be prepared in
situ by nitric acid neutralization of a mixture of
ammonia and potassium hydroxide or carbonate.
The amount of potassium nitrate included in
solid solution in ammonium nitrate in accord-
ance with the present invention may be varied
somewhat depending upon the extent of stabiliz-
ing effect and other properties desired in the fin-
ished explosive.
1Vfetal nitrates, of which potassium nitrate and
sodium nitrate are common and well known
examples, are offert employed as ingredients of
ammonium nitrate explosives. These salts flnd
particular use for oxygen balance adjustment
and for control of flame characteristics. Thi
potassium nitrate employed in solid solution with
ammonium nitrate in accordance with the pres-
ent invention may replace metal nitrate which
would otherwise be employed as an ingredient of
the explosive mix.
Since in some explosives large quantities of
metal nitrate are hot desired, and in New of cost
considerations, if is sometimes desired to limit the

2,602,026

3
quantity of potassium nitrate employed in ac-
cordance with the present invention. It will be
usually round that considerable stabilizing effect
over a Ïairly wide range oÏ temperature fluctua-
tion is still obtained when amounts oÏ potassium 5
nitrate as low as about 4% by weight of the am-
monium nitrate are employed in accordance with
the present invention. ,On the other hand,
amounts of potassium nitrate above about 7.5%
of the ammonium nitrate do hot usually ma- l0
terially aid in increasing the stabilizing and anti-
setting effects obtained by the invention, and
amounts ab0ve about 11% of the ammonium
nitrate will often be found undesirable. Am-
rnonium nitrate containing about 6.5% of potas- 15
sium nitrate is often about optimum for purposes
of the present invention.
The prescrit invention finds application chief-
ly with coarse grained arnmonium nitrates. If
appears fo be only ammonium nitrate of the 20
coarser grain sizes which produces velocity jumps
on temperature fluctuation. Usually the in-
vention wfll be round to bave a diminished
plication when the ammonium nitrate is of a
grain size such that less than about 70% is held 25
on a U. S. S. No. 70 screen.
Since ordinarfly the ammonium nitrate used
in explosives passes a U. S. S. No. 8 screen, the
invention wfll hot generally be applied to am-
monium nitrate of a grain size coarser than this. 30
Explosive liquid nitric esters, such as nitro-
glycerine, with which the ammonium nitrate of
the invention is sensitized, bave, of course, a
detonation velocity of their own. Explosives
containing large amounts of explosive liquid ni- 35
tric ester usually approach the velocity of the
ester. Since the applicability oî the present in-
vention lies largely in the stabflization of the
ammonium nitrate, it wfll be round that the in-
vention bas a diminished utility with explosives 40
having high explosive liquid nitric ester contents.
ttowever, the effectiveness of the invention is
usually retained fo considerable degree in ex-
plosives containing as high as about 20% of ex-
plosive liquid nitric ester. On the other hand 5
contents below about 3 % of explosive liquid ni-
tric ester do hOt usually give sufficient sensitiz-
ing effects for commercial explosives.
The invention wfll be further described by the
following examples which illustrate specific cm- 50
bodiments:
EXAIVIPLE 1
An aqueous solution containing a solids con-
tent of 92.7% arnmonium nitrate, 6% potassium 55
nitrate (about 6.5% based on ammonium ni-
trate), 1% ammonium chloride, and 0.3% am-
monium sulphate was evaporated until it had a
crystallization temperature (fudging point) ol
about 308 ° F. The molten mass was then run 60
into a jacketed crystallizing kettle where it was
cooled with agitation until a dry grained
material resulted. The grained product was
screened through a U. S. S. No. 8 screen, and
the small residue of lurnp material was dis-
carded. Not more than 2% of the material pro-
duced passed a U. S. S. No. 70 screen.
EXAIVIPLES 2 THROUGH 7
Several explosive compositions were ruade up 70
in conventional dynarnite mixers and were
packed in I/2 '' by 8" paper cartridges.
detonaion velocities of some oï these cartridges
were determined in the open and when confined
by tamping inte I/2 '' dimeter, open-ended, steel 75

4
pipe. Other of the cartridges were then cycled
by heating them to 117 ° F. for 7 hours and cool-
ing to @bout 40 ° F. for 16 hours. The confined
detonation velocities of the cycled cartridges
were then measured. Coz-qned detenation ve-
locities were also determined ater a similar
second and third cycle. The composition of the
powders and the velocities obtained are tabulated
below:

Table I

2
8.80
H. 20

Nitroglycerine percent ......
Coarse Ammonium Nitrate
Percent ...................
Coarse Potassium Ammo-
nium Nitrate Percent
(Product o Examplc 1)
Fine Ammonium Nitrate
Percent ................... 2. 50
Sodium Nitrate Percent ..........
PotoEssium Nitrate Perccnt .......
Ycllow Corn Flour Percent_ 4.75
Fine Apricot Plt Pulp
Percent .........................
Wood Pulp Percent ........ 2.25
Chalk Percent .............. 0.50
Car tridges/50# .............. 94. 1
Open Velocity (ft./scc.) ..... 17, 000
Confined Vclocity:
As ruade (ft./scc.) ....... 7, 600
] cycle (ft./scc.) ......... 8, 200
2 cycles (ft./scc.) ........ 8, 800
3 cycles (ft,scc.) ........ 9, 400

Exam' fie--
3 4 5 6
8.80 8.80 6.0 6.0
...... 6.20 80.4 ......

7
6.0
80. 4

81.20 ...........
2.50 2.50 .....
........... 5.0 I
..... 5. 0 .....
4.75 4.75 2.0
...... 4.1
2.25 2.25 2.0
0.50  0.50 0.5 I
94.7 I 92.7 96.0
5, 400
, 800
6, 800 /
7,600/7,700 5 900 [
7,600 1,800 16,9001
, 200 7, 200 :
7, 700 l , 600 8, 000
8, 000

85. 4 ......
::--ï--'-I
2.0 I 2.0
4.1 4.1
2.0 2.0
0.5 0.5
98. 1 95. 7
, 300 5, 400
5, 600 5, 900
5, 300 7, 700
5, 800 8, 700
5, 800 ] 9,500
I

If will be noted tl]at the powder made with
mixed grain potassium and ammonium nitrate
(Examples 3 and 6) in each case showed a sta-
bflity fo cycling. The powder ruade without po-
tassium nitrate (Examples 1 and 5) or with po-
tassium nitrate merely in mechanical admixture
(Examples 4 and 7) jumped in velocity on
cycling.
EXAMPLES 8 THR, OUGH 10
To show the effects of varying amounts of
potassium nitrate in solid solution in ammonium
nitrate, preparations of arnmonium nitrate simi-
lar to those of Example 1 but containing about
4.75% and about 10% of potassium nitrate, based
on ammonium nitrate, were made. These
terials were made up into powder and tested
for detonation velocity as in Examples 2 through
7, except that cycling tests for Example 8 were
ruade between 117 ° F. and 65 ° F. and also
tween 117 ° F. and 8 ° F., and the cycling tests for
Examples 8 and 9 were ruade between 117 ° F.
and 8 ° F. The formulae and results are tabulated
below:

7'able II

Nitroglycerine percent ..........................
Coarse Potassium Ammonium Nitrate percent:
(4.75% I(N O) ..............................
65 (10% K:NOD ................................
Wood Pulp percent .............................
Yellow Corn Flour percent ......................
Fino Apricot Pit Pulp percent ..................
Chalk percent ..................................
Cartridgcs/50# ..................................
Open Veloeity (ft./sec.) .........................
C onfined Velocity:
As marie ....................................
1 cycle (117 ° F.-65 ° F.) .....................
2 cycles (117 ° F.-65  F.) ....................
3 cycles (117 ° F.-65 ° F.) ....................
1 cycle (117 ° F.-8 ° F.) ......................
2 cycles (117 ° F.-8 ° P.) .....................
3 cycles (117 ° P.-8 ° F.) .....................

Example--
8 9 10
8.80 8.80 6.0
3. 60 ............
83. 60 85. 4
.- 2. 25 z o
4.75 4.75 2.0
I00.9 98.9 102.1
6, 300 6, 500 5, 300
7, 400 7, 600 5, 700
7, 800 ...... , ......
7. 500 ..............
71300  .............
7300 7700 ,I00
8',100 7:400 6,000
8,700 7, 500 5, 909

It will be seen from Example 8 that the small
amount (4.5%) of potassium nitrate was suï-
flclent fo stabilize velocity on cycling between
117 ° F. and 65 ° F. but was hot suflicient fo pre-
vent a velocity fise when cycling was conducted
between 117 ° F. and 8 ° F. On the other hand,
it may be seen from Examples 9 and 10 that
the larger amount of potassium nitrate (10%)
was sufficient fo stabilize against velocity in-
crease even for the more drastic cycling between 10
117 ° F. and 8 ° 1 .
EXAM:PLES 11 AND 12
To show the effect of potassium nitrate-am-
monium nitrate solid solutions for stabilizing 15
the velocity of powder made up with a higher
percentage of nitroglycerine, the powders tabu-
]ated below were made up and tested. The
cycling tests were conducted between 117 ° F.
and 40 ° F., and the potassium ammonium nitrate 20
was ruade in accordance with the method of
EXample 1.

Table III

Nitroglycerino Per cent ....... . ...................
Coarse Ammonium Nitrate Per cent ..............
Coarse Potassium Ammonium Nitrate Per cent
(Product of Example 1) .........................
Ffne Apricot Pif pulp Per cent ....................
Bsgssss Per cent ..................................
Wood Pulp Per cent ..............................
Chalk Per ceint ....................................
Cartridges/50#. ....................................
Open Velocity (ft./sec.) ............................
Conflnsd Veloeity:
As ruade ......................................
2 cycles .......................................
3 cycles .......................................
4 cycles .......................................

Exumple-- 25

11
15.0
74. 2

1.0 1.0
4.0 : 4.0
1.0 1.0
99.1 99. 2
8,100 8, 000
9, 800 8, 800
9, 700 9, 300
10,100 9, 300
10, 800 9, 000

It may be seen that even with 15% nitro-
glycerine the ammonium nitrate containing
potassium nitrate in solid solution stabilized the
powder against velocity jump on oonfinement
and on cycling.
What is claimed is:
1. An explosive comprising coarse crystallized
granules consisting of a solid solution comprising
ammonium nitrate and from about 4 % to about
11%, based on ammonium nitrate, of potassium
nitrate uniformly distributed throughout their
structure, said crystallized granules being sensi-
tized with an explosive liquld nitric ester.
2. An explosive comprising crystallized gran-

6
ules consisting Of a solid solution comprising am-
monium nitrate and from about 4 % to about II %,
based on ammonium nitrate, of potassiui ni-
trate uniformly distributed throughout their
5 structure, said crystallized granules being of a
size such as to pass a U. S. S. No. 8 screen and
be held to the extent oï at least about 70% on a
U. S. S. No. 70 screen, and said crystallized gran-
ules being sensitized with up fo about 20% of an
explosive liquid nitric ester.
3. An explosive comprising crystallized gran-
ules consisting of a solid solution comprising am-
monium nitrate and from about 4% to about
11% of potassium nitrate uniformly distributed
throughout their structure, said crystallized
granules being oï a size such as fo pass a U. S. S.
No. 8 screen and be held to the extent oï at least
about 70% on a U. S. S. No. 70 screen, and said
crystallized granules being sensitized with from
about 3% to about 20% of an explosive liquid
nitric ester.
4. An explosive according to claim 3 in which
the content oï potassium nitrate in solid solution
with said ammonium nitrate in said crystallized
granules is about 6.5,%.
JAMES A. FAIR.
12
REFERENCES CITED
15.o The following references are of record in the
........ 30 file of this patent:
74. 2 UNITED STATES PATENTS

Number
1,671,792
35 1,743,172
1,908,569
1,920,438
2,063,572
2,130,712
4O 2,199,218
2,314,806
2,333,637
2,358,384

45 Number
573,147

Name Date
Stoops ............. May 29, 1928
Ward .............. Jan. 14, 1930
Stoops .............. May 9, 1933
Spaeth ............. Aug. 1, 1933
Woodbury .......... Dec. 8, 1938
Cairns ............ Sept. 20, 1938
Cook .............. Apr. 30, 1940
Winning .......... IVfar. 23, 1943
Carey .............. Nov. 9, 1943
Davis ............. Sept. 19, 1944
IOP, EIGN PATENTS
Country Date
Great Britain ........ Nov. 8, 1945
OTHER REFEENCES

Bebie, "Manual of Explosives, iVfilitary Pyro-
50 technics and Chemical Warfare Agents," pub-
lished 1943 by MacMillan & Company, New York,
Pages 25 and 26.