The present invention relates to a novel process for the preparation of
long delay detonator compositions and long delay detonator compositions
prepared thereby.
BACKGROUND OF THE INVENTION
Long delay detonator compositions comprise normally a combination of
oxidizers, fuels and diluents. The oxidizer normally used is red lead
while fuels used are silicon of different particle sizes and selenium. The
diluent is normally barium sulphate.
Conventional processes for the preparation of long delay detonator
compositions involve physically mixing the different ingredients. The
Inversion Burn Rate (IBR) of such compositions prepared by physically
mixing is relatively low' The delay detonator compositions obtained,
therefore, have very low delay times. The process of physically mixing is
inherently unsafe since it involves the handling of silicon and selenium.
The processes is less reliable since critical parameters such as the
stirring speed which help to control the mixing efficiency and the rate of
addition of various components cannot be controlled or quantified.
Also, since the long delay detonator compositions obtained by physically
mixing have very low delay times, long delay element lengths had to be
necessarily longer.
OBJECTIVES
It is an object of the present invention to provide a novel process for the
preparation of long delay detonator compositions with longer delay times
and longer IBRs.
It is an object of the present invention to obtain long delay detonator
compositions which have substantially longer delay times than prior art.
It is also an object of the present invention to obtain detonators with
delay times which were not obtainable by physically mixed compositions.
It is another objection of the invention to obtain a long delay detonator
composition wherein the delay times achievable with physically mixed
compositions can now be achieved by smaller delay element lengths.
It is an object of the present invention to provide a process for the
preparation of long delay detonator compositions which are safer in
terms of handling, more reliable and allow the control of critical process
parameters as well as the rate of addition of the various ingredients.
SUMMARY OF THE INVENTION
It has now been found that long delay detonator compositions with
substantially longer delay times can be obtained by wet mixing using a
novel co-precipitation method.
Accordingly, the present invention provides a novel process for the
preparation of long delay detonator compositions comprising adding red
lead, silicon of varying particle sizes and selenium to a solution of
stochiometric amount of barium chloride dissolved in water along with a
dispersant in order to precipitate barium sulphate, vigorously stirring the
slurry so obtained and adding a solution of a stochiometric amount of
sulphate in water slowly to the slurry to obtain co-precipitated material,
recovering the precipitation in any conventional manner in order to
obtain the final delay composition.
The co-precipitation technique involves the precipitation of BaSO4 along
with the other constituents of the delay composition by the addition of
red lead, silicon (of the two different particle sizes) and selenium to a
solution of the stochiometric amount of barium chloride dissolved in the
requisite amount of water, along with a small quantity of a conventional
dispersant. The slurry is vigorously stirred and a solution of the
stochiometric amount of (NH4)2SO4 in the requisite amount of water is
then added slowly to it to give the co-precipitated material. This
precipitate is filtered, washed with water, dried and powdered to give the
final delay composition. This material can then be directly used for
making the delay elements in the long delay detonator.
Normally, the amount of barium sulphate in the final composition is from
21.6% to 42.6%, red lead is from 47% to 61%. Silicon having a particle
size of 1 micron is optionally present. Silicon having a particle size of 6
microns may comprise a proportion of 6% to 17.5% while selenium may
be optionally included in the composition.
In a preferred embodiment, silicon (<1µ) is present in a proportion of
1,8% to 3.25% and selenium is present in a proportion of 0.9% to 2.6%
by weight.
A preferred mode of working the process is to add red lead, silicon (of
different particle sizes) and selenium to a solution of the stochiometric
ammonium of barium chloride in the requisite amount of water along
with a small quantity of a conventional dispersant to precipitate barium
sulphate and then vigorously stir this slurry. The solution of
stochiometric ammonium sulphate in the requisite amount of water is
then added slowly to obtain co-precipitated material. This precipitated
material is filtered, washed with water, dried and powdered to obtain the
final delay composition. The composition finally obtained displays
extremely high inversion burn rates compared to the prior art and can be
used directly to make delay elements in a long delay detonator
composition.
Characterization of the co-precipitated material by methods such as X-
ray, photoelectron spectroscopy, laser diffraction particle size analysis,
electron diffraction and by energy dispersive X-ray analysis shows that
individual particles of the co-precipitated material may contain some or
all of the constituents of the mixture.
It is, therefore, possible to obtain delay detonators with delay times
which were previously not obtainable by physically mixed composition by
using similar delay element lengths.
For instance, a long delay element having the composition, barium
sulphate 42.6%, red lead 47.2%, silicon (<1µ) 1.8%, silicon (6µ) 7.5% and
selenium 0.9%. when prepared by the method of physical mixing has an
Inverse Burn Rate of 125 ms/mm but the same composition when
prepared by the co-precipitation technique gives an IBR of 210 ms/mm.
Also, it is evident from the IBRs of different compositions prepared under
different conditions where the molarity and rate of addition of
ammonium sulphate have been varied (Table 1,2), that the co-
precipitated compositions have much higher IBRs than the identical
compositions prepared by the existing method of physically mixing the
constituents.
The co-precipitation technique is unique in that it involves wet mixing in
contrast to the dry mixing as in the case of conventional methods of
physically mixing. This ensures greater safety in the handling of silicon
and selenium. The wet mixing also ensures that critical parameters such
as stirring speed which ensures control of the mixing efficiency and the
rate of addition of ammonium sulphate can be quantified and controlled.
The co-precipitation method of the invention is, therefore, more reliable.
It must be noted that the novelty resides in the process and not in the
final composition obtained. Thus, it is possible to obtain compositions
with varying percentages by using this novel process. The proportions
given hereinabove are merely examplary.
Example 1:-
For making a long delay composition on a 5 kg batch scale the following
procedure was used.
To a 7.5 liter, of molar barium chloride solution, red lead = 2.75 kg,
silicon (6µ - particles) = 0.3 kg, silicon (< 1 µ - particles) = 0.125 kg,
selenium = 0.075 kg, dispersant = 0.050 kg, were added. Stirring was
started to homogenize the slurry. Then 7.5 liter of 1 molar ammonium
sulphate solution was added with a metering pump a the rate of ~ 150
ml/min. After the addition was over, stirring was continued for another
30 minutes. The slurry was then filtered and washed with 6 liter of
water. The wet cake was then dried at 60°C for 12 hours, delumped and
sieved to get a 240 mesh (d=40 µ) powdered material which was then
used for making the delay detonators. The IBR of this composition was
180 ms/mm whereas the IBR of the identical composition prepared by
physical mixing was 62 ms/mm.
The above example is merely illustrative of the present invention and is
not a limitative of the scope thereof. It is possible to vary proportions of
various ingredients in the final composition while still using the process
of this invention.
WE CLAIM:
1. A novel process for the preparation of a long delay detonator
composition comprising:
i. precipitating barium sulphate by adding red lead, silicon and
optionally selenium to a solution of stochiometric amount of
barium chloride in water;
ii. stirring said slurry and then adding a solution of the
stochiometric amount of ammonium sulphate in water
slowly in order to obtain a co-precipitated material; and
iii. recovering the material precipitated by any conventional
manner in order to obtain the final delay composition.
2. A process as claimed in claim 1 wherein said silicon may be of two
different particle sizes of less than 1 µand less than 6 µ.
3. A process as claimed in claim 1 or 2 wherein said silicon has a
particle size of less than 6 µ.
4. A process as claimed in claim 1 wherein said selenium is optionally
present.
5. A process as claimed in claim 1 wherein the molarity of ammonium
sulphate to that of barium chloride is 1 to 0.5:1.
6. A process as claimed in any preceding claim wherein the rate of
addition is between 5 to 10 ml. per minute.
7. A novel process as claimed in any preceding claim wherein the
precipitated material is recovered by filtering washing with water
and subsequently drying at a temperature of 60°C to obtain a dried
cake.
8. A novel process as claimed in claim 7 wherein said dried cake
obtained is powdered in any conventional manner.
9. A process as claimed in any preceding claim wherein said
conventional additive is a convention dispersant.
10. A long delay detonator composition whenever obtained by the novel
process as claimed in any preceding claim comprising 21.6 to
42.6% barium sulphate. 47.2 to 61% red lead, 6 - 17.4% silicon
(<6 µ), 0-3.25% of silicon (< 1 µ), 0 to 2.6% selenium and the
balance, if any comprising one or more conventional additives.
11. A long delay detonator composition substantially as hereinbefore
described and with reference to the foregoing Examples.
12. A novel process for the preparation of a long delay detonator
composition substantially as hereinbefore described and with'
reference to the foregoing Examples.
Dated this 15th day of January, 1996.

It has now been found that long delay detonator compositions with
substantially longer delay times can be obtained by wet mixing using a
novel co-precipitation method.
Accordingly, the present invention provides a novel process for the
preparation of long delay detonator compositions comprising adding red
lead, silicon of varying particle sizes and selenium to a solution of
stochiometric amount of barium chloride dissolved in water along with a
dispersant in order to precipitate barium sulphate, vigorously stirring the
slurry so obtained and adding a solution of a stochiometric amount of
sulphate in water slowly to the slurry to obtain co-precipitated material,
recovering the precipitation in any conventional manner in order to
obtain the final delay composition.

The co-precipitation technique involves the precipitation of BaSO4 along
with the other constituents of the delay composition by the addition of
red lead, silicon (of the two different particle sizes) and selenium to a
solution of the stochiometric amount of barium chloride dissolved in the
requisite amount of water, along with a small quantity of a conventional
dispersant. The slurry is vigorously stirred and a solution of the
stochiometric amount of (NH4)2SO4 in the requisite amount of water is
then added slowly to it to give the co-precipitated material. This
precipitate is filtered, washed with water, dried and powdered to give the
final delay composition. This material can then be directly used for
making the delay elements in the long delay detonator.
Normally, the amount of barium sulphate in the final composition is from
21.6% to 42.6%, red lead is from 47% to 61%. Silicon having a particle
size of 1 micron is optionally present. Silicon having a particle size of 6
microns may comprise a proportion of 6% to 17.5% while selenium may
be optionally included in the composition.
In a preferred embodiment, silicon (<1µ) is present in a proportion of
1.8% to 3.25% and selenium is present in a proportion of 0.9% to 2.6%
by weight.
A preferred mode of working the process is to add red lead, silicon (of
different particle sizes) and selenium to a solution of the stochiometric
ammonium of barium chloride in the requisite amount of water along
with a small quantity of a conventional dispersant to precipitate barium
sulphate and then vigorously stir this slurry. The solution of
stochiometric ammonium sulphate in the requisite amount of water is
then added slowly to obtain co-precipitated material. This precipitated
material is filtered, washed with water, dried and powdered to obtain the

final delay composition. The composition finally obtained displays
extremely high inversion burn rates compared to the prior art and can be
used directly to make delay elements in a long delay detonator
composition.