CA1062470A - Method of manufacturing a non-sensitive aqueous gel suspension explosive - Google Patents

Abstract

METHOD OF MANUFACTURING A CAP-SENSITIVE AND NON-SENSITIVE
AQUEOUS GEL SUSPENSION EXPLOSIVE
Abstract of the Disclosure Non-cap sensitive aqueous gel explosives contain-ing no suspended solid fuels are made by combining water, hexa-methylenetetramine, ammonium nitrate, sodium nitrate, ammonium perchlorate and nitric acid, along with sufficient polysac-charide gum to thicken the mixture.

Description

~L~62470 .

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This application is a divisian of Canadian Patent App~ication Serial No. 247,465 filed March 9th, 1976.
Aqueous gel explosives which derive their ~ chemical energy mainly from thermal decomposition of ammonium ;~ nitrate are used extensively in quarrying, excavating and mining, primarily because they are cheap and safe to handle.
These explosives usually contain expensive suspended solid fuels and cannot be detonated with blasting caps, but require ;~ substantial high explosive booster charges to obtain efficient detonation. There are needed both cheaper non-cap sensitive explosives containing no solid fuels or sensitizers and also explosives that can be placed and detonated in a manner similar : ;:
to dynamite, but which are cheaper and much less prone to accidental detonation. We have discovered that a class of ''~ aqueous gel explosives based on ammonium nitrate suspensions 'l~ can readily be made without the use of suspended solid fuels and `'i can also be con~erted to cap sensitive form, in which they will serve as relatively safe substitutes for dynamite.
~ Gelled aqueous ammonium nitrate suspension Y;l~ 20 explosives are known. In U. S. Patent 3,676,236 of Klima et al there are disclosed explosive compositions made up of ~arying proportions of ammonium nitrate, sodium nitrate, ammonium perchlorate, hexamethylenetetramine, nitric acid, a inely divided solid fuel, a hydroxy-substituted thickening agent and a ~ cross-linking agent. The prior art explosive compositions are ,.,~

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particularly useul for placement in rather large, widely spaced drill holes such as are customarily found in open pit hard rock mining. Explosives of this type are customarily , ,.
: detonated by means of blasting caps and high explosive booster .:, ~
charges.
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We have found that non-cap sensitive explosives ~ can be manufactured, using the same ingredients as employed ,~ in the prior art but without the necessity of including a finely ~ij........... divided solid fuel therein, providing the proportions of in~re-:~;;^ 10 dients are kept wi~hin narrow ranges, according to the ;. following procedure: :
:.~` (a) preparing a mother liquor consisting o 26 to 36 weight percent water, from 14 to 24 weight percent hexa-methylenetetramine, from 30 weight percent to a sufficient '~ quantity of ammonium nitrate to saturate the solution, from S to :
15 weigh* percent ammonium perchlorate and~sufficient nitric acid to obtain~a pH of 4.0 to 6.5 and, (b) adding from 80 to 175:parts by weight of particulate~ammonium nitrate to each :100 parts of mother ;20 :~ liquor~prepared in~step (s) so as to bring the total water content of the resulting composition to within 13 to 18 weight percent, along with sufficient polysaccharide gum to thicken i .~",........ . . .
the mixture to a gel consistency. :

~i'J The mother liquor for use in step (a) above may ~ be prepared as follows::

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`, ~ixing with a 30 to 40 weight percent aqueous , ., ~
~; solution of hexamethylenetetramine, sufficient nitric acid to obtain a pH of 5.0 to 5.3, while :~.
~ controlling the temperature of the resulting . .
mixture so that it does not rise above 66C, so as to produce an aqueous solution in which .
the hexamethylenetetramine content is from 25 to 35 weight percent, then in a quantity of this solution dissolving suficient ammonium perchlorate to yield a ~; ~ final concentration of from 5.0 to 6.0 percent, sufficient sodium nitrate to yield a final concentration of 8.0 to 9.0 percent and sufficient ammonium nitrate to yield a final . concentration of 30 to 45 percent.
With this mother li~uor there may then be mixed preferably finely ground particulate ammonium nitrate and sufficient thickening agent to form a non-cap sensitive explosl~e gel in~which the ammonium~nitrate is suspended.
Subsequently,~paint grade aluminum powder or other sensitizing agent may beadded to convert the composition into a cap-, ........................................................................ .
~1 sensitive substitute for dynamite.
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The various steps o~ the method have critical features from which substantial deviation may lead to failure ,; . :
Thé critical aspects of each step are discussed below:

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~ 3 ~062470 STEP (a~

In the beginning of this step an exothermicreaction occurs, if performed as exemplified. Only water, hexamethylenetetramine and nitric acid are preferably present at the beginning so that temperature and pH can be more con-veniently controlled. The upper limit of temperature should be strictly observed to prevent decomposition from occurring ;
as a side reaction. Preferably the temperature is controlled between 50 and 60C. ;
;; 10 Since the dissolving of ammonium nitrate is endothermic, this can be accomplished more quicXly and con~en- :
iently by providing additional heat through a steam coil or other heat exchange means. Preferably, enough heat is supplied during this ~step to yield a final temperature of 35 to 50C
in preparation for step (b).
STEP (b) !;, I ~ . .
I,j' If desired, the~solution produced in step ta) ~" ~
oan be kept in storage and portions of it may be used as mother liquor to prepare a var1ety of explosive products. It ~ is more economical and convenient, however, to use this $,~ solution as it comes from step (a) before it becomes cool.
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; The ammonium nitrate employed ~n this step should be finely ground and free of lumps. ~he combination of polysaccharide ! gum and cross-linking agent should be chosen from among those ` available on the market for the ability to gel a suspension . ,i "

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of the sort produced in this step. Some gums do not produce a sufficiently firm gel at the pH of this suspension (about ;~
5.8-5.9).
STEP (c) '7' It is essential that this sensitizing step is performed only after the suspension of step (b) has become thickened. It is also essential that mixing is stopped as . . ~ .
3`. soon as uniform appearance of the product is achieved. Further ~4':. mixing is dietrimental to sensitivity.
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i lO In the following specific examples there are iS illustrated the preparation of a variety of both cap-sensitive ,., ~ and non-cap-sensitive products.
; r ;~ EXAMPLE 1 In a clean stirred reaction vessel there was placed 8,349 parts of water. To this there was added, with stirring, 4,914 parts of solid particulate hexamethylenetetramine ., i~ and stirring was continued until solution was obtained.
To this solution, there was added 1,988 parts of nitric acid (69%; 42 Baume') while stirring and controlling 20~ temperature within a range of about 45 to 60C during the evolution of heat, continuing mixing after all reaction had ~- ceased, as indicated by stabllity of pH and a decrease in temperature. At this stage the pH measured from 5.1 to 5.3 at 38C.
To this solution there was then added 10,602 parts of prilled ammonium nitrate with stirring, while heating ,~; , ..i ~` -' ~06Z4~0 ." :.
~ the reactor with a steam jacket. While maintaining a tempera-; .
, ture approaching 50C there was also dissolved in the mixture -~ 1,551 parts o$ ammonium perchlorate and 2,586 parts of sodium ." . .
nitrate. Properties o~ the finished solution as measured on ; ~

;: a series of batches prepared as described above, were as -.. ,,~ , :
- follows: ~
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pH 5.8 to 5.9 i-~ Specific gravity 1.34 to 1.35 g/cc ` Crystallization temperature minus 4C
The solution as described above was then employ~d as liquid phase to form a gelled suspension as described below, operating at a temperature between 38 and 49C.
Into a mixing vessel was placed 1,960 parts of . finely ground ammonium nitrate. A suficient quantity of the above-described liquid was then added, with mixing, to form a ` :
slurry which was smooth and free of lumps. The remainder of a total of 2,000 parts of the above-described liquid was then i~ added, with stirring, along with 40 parts of guar gum with cross-linXing~agent which was added through eductors at such a rats that mixing was thorough and no lumps formed. The thickened suspension was allowed to reach gel consistency, .,,.,, ~ . .
which required about eight to ten minutes after addition of guar gum was complete. ~he product consisted of 4,000 parts by weight of a non-cap-sensitive aqueous gel suspension explosive having a density of 1.20 to 1.25 g/cc and a pH between 5.9 and ,; ,~
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. 6.2. The percentages of various components in the finished i. composition (to one decimal place) were as follows: .
~`. INGRED:I~NTS % BY WT. : .
. Water 14.9 Nitric Acid (lOO~i basis) 2.3 .. Hexamethylenetetramine 8.2 Ammonium Nitrate in solution17.7 : .
.
~: Ammonium Perchlorate 2.6 .
i Sodium Nitrate 4.3 ~ 10 Ammonium Nltrate (ground)49.0 .
,' Guar Gum (NGL 4779, New, FF)1.0 ~ (Stein-Hall) with ;.................... Cross Linker RO (Stein-Hall) ~ : EXAMPLE 2 r' ~
Step (a) was perormed according to the method of this invention to y.ield a solution made up rom the ollowing raw materials~:
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; : Hexamethylenetetramine 15.3 weight percent ~ Water ~ 30.6 ;,F~ 2~0 ; ~ :Ni*ric acid~ 6.5 Ammonium perchIorate S.l Sodium nitrate 8.5 ,~; . .
Ammonium nitrate 34.0 :100.0 weight percent ::' ~ ,r~;"~ .

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To 58.8 parts of the above solution was added 36.3 parts of finely ground ammonium nitrate and 0.9 parts of guar gum with cross-linking agent (Stein-Hall NGI. 4779 New, FF with cross-linker RO) with thorough mixing. After the resulting mixture ., -. ~
set to a gel consistency, 4.0 parts of leafing grade aluminum pigment powder was mixed in until a uniform appearance was ;
obtained. Mixing was then s~opped.
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- The product was detonatable with a number 6 :, ` electric blasting cap in a charge having a diameter of 1.25 inches ~3.2 cm) at temperatures as low as minus 17.8C with a detonation ~elocity of 10,000 ft t3,045m) per second. The gel structure of the product conferred excellent water resist~
ance. A~ter storage for three months at 48.9C there was no .
loss of sensitivity or breakdown of gel structure.

i-l EXAMPLE 3 ,~. .
j A series of batches of explosive was made ,......................................................................... .
~i according to the procedure described below:

; In a clean stirred reactor ~essel there was . ~, placed 8,349 parts of water. To this there was added, with 20 ~ stirrlng,~4,91~3 parts of solid particulate hexamethylene-'r~ tetramine and stirring was continued until solution was,~., .
obtained.
To this solution there was added 1,988 parts ofnitric acid (69%: 42 Baume) while stirring and controlling temperature within a range of about 45 to 60C during the .'i', ~
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~162470 evolution of heat, continuing mixing after all reaction had ceased, as indicated by stability of pH and a decrease in ` temperature. At this stage the pH measured from 5.1 to 5.3 at 38C on various batches made by this procedure.
; To this solution there was then added 10,602 parts of prilled ammonium nitrate with stirring, while heatiny -` the reactor with a steam jacket. While maintaining a tempera-~` ture approaching 50C there was also dissolved in the mixture ,A" 1,551 parts of ammonium perchlorate and 2,586 parts of sodium ~ 10 nitrate. Properties of the finished solution as measured on .` a series of batches prepared as described above, were as ,s.~
~ follows:
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~ pH 5.8 to 5.9 i.,.~ , ~`~ Specific gravity 1.34 to 1.35 g/cc fA;j Crystallization temperature minus 4C

''f~ The solution as described above was then employed as liquid , . ~ .
phase to form a gelled suspension as described below, operating at a temperature between 38 and 49C.
Into a mixing vessel was placed 1,480 parts of fLnely ground ammonium nitrate. A sufficient ~uantity of the above-described liquid was then added, with mixing, to form a slurry which was smooth and free of lumps. The remainder of a total of 2,320 parts of the above-described liquid was then added, with stirring, along with 40 parts of guar gum which was added through~eductors at such a rate that mixing was .,. . ~ .
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: thorough and no lumps ~ormed. The thickened suspension was allowed to reach gel consistency during a period of at least ` 5 minutes, while continuing to mix slowly. After gel formation .. , appeared to be complete, then 160 parts of paint pigment grade . aluminum powder was mixed in at low speed until a uniform -~. appearance was obtained. As soon as this appearance was `3l obtained, mixing was stopped. The product was 4,000 parts of a stable, cap sensitive aqueou~ gel explosi~e. Properties of a series of batches made by repetition of this procedure were .~. 10 ~s follows:
~- pH 5.9 to 6.2 .. Specific gravity 1.10 to 1.15 g/cc Classification High Explosive - Class A
` Cap-sensitive at temperatures as low as minus 23~C
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. The product made according to the procedure of .~I, this example was composed of 9.5 percent hexamethylenetetramine, ~ 2.7 percent nitric acid, 57.5 percent ammonium nitrate, 5 .
:."~ percent sodium nitrate, 3 percent ammonium perchlorate, 4 ; ,;.. ~ ~ . :
'1. percent paint pigment grade~aluminum powder, one percent guar gum with crosslinker and water.

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Claims (3)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN
EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS
FOLLOWS:

1. The method of manufacturing a non-cap-sensitive aqueous gel explosive containing no suspended solid fuel comprising the steps:
(a) preparing a mother liquor consisting of 26 to 36 weight percent water, from 14 to 24 weight percent hexamethyl-enetetramine, from 30 weight percent to a sufficient quantity of ammonium nitrate to saturate the solution, from 5 to 15 weight percent sodium nitrate, from 5 to 15 weight percent ammonium perchlorate and sufficient nitric acid to obtain a pH
of 4.0 to 6.5 and, (b) adding from 80 to 175 parts of particulate ammonium nitrate to each 100 parts of the mother liquor prepared in step (a) so as to bring the total water content of the resulting composition to within 13 to 18 weight percent, along with sufficient polysaccharide gum to thicken the mixture to a gel consistency.

2. The non-cap-sensitive aqueous gel explosive made by the process of Claim 1.

3. The non-cap-sensitive aqueous gel explosive made by the process of Claim 1, composed of 8.2 percent hexamethylenetetramine, 2.3 percent nitric acid, 66.7 percent ammonium nitrate, 4.3 percent sodium nitrate, 2.6 percent ammonium perchlorate, one percent guar gum with crosslinker and water.