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Full text of "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.