Note: Descriptions are shown in the official language in which they were submitted.
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DESENSITISATION OF ENERGETIC MATERIALS
This invention relates to the desensitisation of energetic crystalline
materials, in
particular hexanitrohexaazaisowurtizane (HNIW) (also designated CI-20) but
also
other nitramine explosives such as cyclotrimethylene trinitramine (RDX) and
cyclotetramethylene tetranitramine (HMX).
HNIW comprises a high density caged molecule recognised as a suitable
energetic filler for propellant materials and explosives. Its use as a
potential
replacement for
existing fillers such as RDX and HMX in cast double base, composite and novel
propellants and other explosive materials has been postulated.
Propellant compositions used for launching relatively high mass projectiles
are
desirably highly energetic and energetically dense i.e. a small volume of the
material will produce high potential kinetic energy via rapid gasification on
ignition.
In general, such a propellant composition comprises three component materials;
an energetic filler, a plasticiser and a binder, the latter two components
primarily
provide the desirable mechanical properties of the resultant propellant
material.
Choice of plasticiser and binder for a particular energetic filler will depend
on a
number of factors such as the projection range for the projectile, the
extremes of
temperature under which the end product is expected to operate and the
chemical
and physical interactions of the materials.
However, aside from the functional performance of the propellant material as
an
end product, industrial manufacturers of novel materials must consider the
safety
issues associated with the incorporation and manufacture of these filler,
binder or
plasticiser materials into rocketry. Thus, whilst from a performance point of
view an
energetic material may appear desirable for use as either a binder,
plasticiser or
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filler in the predicted propellant formulation, the material must be safe for
incorporation, processing and transportation. If an unsafe energetic material
was
to be incorporated into a propellant or explosive system, the unsafe material
might
initiate during either the manufacturing process or during transportation of
the end
product. This initiation might be via accidental friction or impact
stimulation
leading to deflagration or possibly a deflagration to detonation transition
within the
explosive material sufficient to cause an unwanted premature explosion. For
this
reason of safety, most known propellant materials (e.g. Ammonium Perchlorate /
hydroxy terminated polybutadiene based composite propellant) comprise,
comparatively, energetically inert plasticiser and binder components.
In general, solid propellant materials such as those based on Ammonium
Perchlorate, Hydroxy terminated polybutadiene (binder) and dioctyl sebacate
(plasticiser) are manufactured by a dry mixing and blending process : this
means
that no additional desensitising solvent s (e.g. water) are added to this mix
other
than those that will be incorporated into the final propellant formulation.
This dry
mix, once manufactured, is treated to facilitate curing of the binder material
to
provide the desirable mechanical properties for the propellant material. This
method is generally considered preferable to a wet mixing process (where
additional solvent is included as transport media or processing aid or as a
desensitiser to improve safety) as it provides better homogeneity of mixing,
and
minimises delays in cleaning mixing equipment or drying out of the mixed end
product prior to further processing (e.g. casting and curing).
Typically, existing propellant materials comprise around 6% by weight
plasticiser
to 85% by weight energetic filler. The propellant material will also generally
comprise around 9% by total weight of binder and other filler materials.
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HNIW is a highly friction sensitive material
having a rotary friction test Figure of Friction (F of F) of
0.7 and produces a highly ferocious response on reaction via
friction stimuli. The exceptionally low F of F of HNIW
(when compared against other ingredients routinely used in
propellant/explosive formulations) poses a considerable risk
in the initial process of dry mixing the plasticiser, binder
and filler, as is conventional in solid propellant
manufacture. The low F of F value excludes the use of CL20
in large scale propellant manufacture in some explosive
companies. Thus, the manufacturer is challenged with the
task of providing a safe process by which HNIW can be
incorporated into explosive and propellant materials whilst
having minimal effect on the overall performance
characteristics of the end product.
The invention relates to an intermediate material
for a propellant composition, the intermediate material
being in powder form and comprising from 90 to 99 weight
percent of a particulate energetic crystalline material and
from 1 to 10 weight percent of an energetic plasticiser
material, the energetic plasticiser material substantially
coating the individual particles of the energetic
crystalline material.
In the first aspect, the invention is an energetic
material comprising an energetic crystalline material
substantially coated in an energetic plasticiser material.
Preferably the energetic crystalline material is
particulate, the energetic plasticiser substantially coating
individual particles of the energetic crystalline material.
The energetic material is advantageously in powder
form, the powder comprising particles of energetic
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crystalline material substantially coated in an energetic
plasticiser material.
Advantageously the energetic material comprises
from 90 to 99% by weight of an energetic crystalline
material and from 1 to 10% by weight of an energetic
plasticiser material.
The inventors have found that the combination of
just a small quantity of energetic plasticiser material to
the energetic crystalline material prior to incorporation
into the bulk plasticiser, binder and filler mixture of an
explosive or propellant
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composition has two unexpected and advantageous effects. Firstly, plasticiser
addition leads to a reduction in the friction sensitivity of the energetic
crystalline
material to equivalent or less than that of many commonly used energetic
filler
materials such as ammonium perchlorate and secondly, the plasticiser addition
also results in reduced ferocity of response on stimulation . The resultant
novel
intermediate of the energetic crystalline material and plasticiser can then be
more
safely used as a starting material for the dry mixing/blending/curing
processes
previously described used in the manufacture of known propellant and explosive
compositions. These novel intermediate, plasticiser added, energetic
crystalline
material products are also more safely handled and transported than the pure
energetic crystalline material.
In one particular method in accordance with the present invention, to
manufacture
an energetic material comprising an energetic crystalline material/energetic
plasticiser mix, desirably the energetic crystalline material and energetic
plasticiser
material are mixed via a wet mixing process with the plasticiser material
being
added to, for example, water wet HNIW. The inherent characteristics of wet
mixing reduces the friction arising within the mixture during the mixing
process and
thus minimises the risk of explosive reaction in the energetic crystalline
material by
friction stimuli. After mixing, the water wet, plasticised energetic
crystalline material
mix can be left to dry to a powdery state, the resultant dry powder formed
being
finely coated with the energetic plasticiser component. The resultant
energetic
crystalline material/energetic plasticiser mixture formed is a relatively
friction
insensitive energetic material when compared against pure, dry energetic
crystalline material.
The inventors have found that the combination of just a small quantity of
plasticiser
material to an energetic crystalline material such as HNIW in manufacture of
an
explosive or propellant composition has an unexpected and advantageous effect
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of reducing the friction sensitivity of HNIW to equivalent or less than that
of
commonly used energetic filler materials such as Ammonium perchlorate or HMX.
The resultant novel intermediate products manufactured by this desensitisation
method can then be more safely used as a starting material for the dry
mixing/blending/curing processes conventionally used in the manufacture of
known propellant and explosive compositions. These novel intermediate products
are also more safely handled and transported than the pure product. Another
unexpected yet advantageous characteristic of these novel materials is that,
once
initiated, they display a reduced ferocity of response compared to that of the
pure
product.
The energetic plasticiser is preferably selected from the group comprising
Butane
Trios trinitrate (BTTN), Trimethylanol ethane trinitrate (TMETN),
Diazidonitrazapentane (DANPE), Glycidyl Azide Polymer (Azide Derivative) (GAP
Azide), Bis(2,2-dinitropropyl)acetal / bis(2,2-dinitropropyl)formal (BDNPA/F)
or
mixtures of two or more of these plasticisers. As well as bringing about the
desired
desensitisation effect, these plasticisers add energy to the propellant system
compared to the use of inert analogues. As a consequence, the intermediate
material produced has a higher energy density compared to inert analogues :
this
is a desirable characteristic of materials for use in rocketry / explosive
programs as
all constituents of the subsequent explosive / propellant formulation
manufactured
using the intermediate contribute energetically to the final formulation. The
use of
energetic crystalline materials desensitised with energetically inert
plasticisers
would have comparatively less energy than that of the proposed, energetic
plasticisers formulations.
The energetic plasticiser material may comprise 100% of any of the
plasticisers
listed above, mixtures of those plasticisers listed above or optionally may be
a
blend of energetic plasticiser and a binder material (e.g. Poly(3-
Nitratomethyl-3-
...........................
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Methyloxetane) (PolyNIMM ), Poly Glycidyl Nitrate (PoIyGLYN) or Glycidyl Azide
Polymer (GAP)) of proportions encompassing from minimum quantity of 10% by
weight plasticiser to 90% binder, to 100% plasticiser to 0% binder. The term
"energetic plasticiser material" as referred to hereinafter should be
construed
accordingly with the above description.
Preferably, the novel energetic material will comprise between 1 % and 5% by
weight of energetic plasticiser material and most preferably between 3% and 5%
by weight of energetic plasticiser material.
For mixed binder / plasticiser systems, preferably the energetic plasticiser
material
will comprise between 30% and 100% energetic plasticiser and 70% to 0% binder.
Most preferably the plasticiser content will be in the range 60% to 100%.
Thus the present invention provides a method for manufacture of a highly
energetic, intermediate material based on a energetic crystalline material
desensitised for safe incorporation into propellant or explosive formulations.
In a second aspect, the present invention provides a method for manufacture of
a
propellant material containing an energetic crystalline material comprising;
(i) mixing 1 to 10% by weight of an energetic plasticiser material with 99 to
90% by weight of the energetic crystalline material,
(ii) mixing and/or blending the resultant product of step (i) with additional
quantities of plasticiser and binder material as appropriate for the end
application of the propellant material,
(iii) curing the resultant product of step (ii).
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The energetic plasticiser material preferably contains a plasticiser selected
from
Butane Triol trinitrate (BTTN), Trimethylanol ethane trinitrate (TMETN),
Diazidonitrazapentane (DANPE), Glycidyl Azide Polymer (Azide Derivative) (GAP
Azide), Bis(2,2 - dinitropropyl) acetal / bis (2,2 - dinitropropyl) formal
(BDNPA/F) or
mixtures of two or more of these plasticisers.
In a third aspect the invention is an explosive or propellant composition made
from
a an energetic material comprising;
(i) from 90 to 99% by weight HNIW; and
(ii) from 1 to 10% by weight of an energetic plasticiser material comprising a
plasticiser selected from the group comprising; Butane Triol trinitrate
(BTTN), Trimethylanol ethane trinitrate (TMETN), Diazidonitrazapentane
(DANPE), Glycidyl Azide Polymer (Azide Derivative) (GAP Azide), Bis(2,2-
dinitropropyl)acetal / bis(2,2-dinitropropyl)formal (BDNPA/F), or mixtures of
two or more of these components.
In order to more fully illustrate the novel methods, products and applications
of
this invention and their associated advantages, experimental data for some
specific embodiments of the invention are now given by way of exemplification
only. Although all analyses were carried out using Epsilon form HNIW, it is
anticipated that this method of desensitisation would be effective on other
crystal
polymorphs of HNIW as well as known energetic crystalline materials such as
cyclotrimethylene trinitramine (RDX) and cyclotetramethylene tetranitramine
(HMX).
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1) Rotary friction testing of HNIW in the Epsilon crystal form was carried out
and a Figure of Friction (FofF) = 0.7 was achieved. The sample response
during testing was a violent report and flash.
2) 0.25g of TMETN stabilised with 1% 2-Nitrodiphenylamine (2NDPA) was
added to 5g of dry Epsilon form HNIW and mixed. The material formed was
a light orange powder. The material was assessed by rotary friction and the
FofF achieved = 2.2. In addition to the reduction in friction sensitiveness,
the violence of response was reduced from a violent report / flash for the
pure
HNIW material to a mild report without flash.
3) Replicate analysis of the formulation example given in example 2 were
carried out with the substitution of TMETN with BTTN, a mixture of BTTN
and TMETN, DANPE, GAP Azide, BDNPA/F, PolyNIMMO, PoIyGLYN and GAP.
All materials appeared as white / yellow powders. For these mixtures, the
friction sensitiveness determined were established as given in Table 1.
Table 1
Sample FofF
CL20 : TMETN 2.2
CL20 : BTTN 2.1
CL20 : BTTN / TMETN (50/50) 2.4
CL20 : GAP Azide 2.1
CL20 : DANPE 1.9
CL20 : PoIyGLYN 2.2
CL20: PolyNIMMO 1.9
CL20 : GAP 1.64) Replicate analysis of the formulation given in example 2 were
carried out
but with the substitution of TMETN with mixed binder : plasticiser
formulations.
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All mixtures formed white / light yellow powders. For these mixtures, the
friction
sensitiveness determined were established as shown in Table 2:
Table 2
Solid Binder Plasticiser FofF
CL20 PoIyGLYN GAP Azide 2.7
CL20 PoIyGLYN DANPE 2.5
CL20 PoIyGLYN BTTN / TMETN (80:20) 2.7
CL20 PoIyGLYN BDNPA/F 2.1
CL20 PolyNIMMO GAP Azide 2.9
CL20 PolyNIMMO DANPE 2.9
CL20 PolyNIMMO BTTN / TMETN (80:20) 3.1
CL20 PolyNIMMO BDNPA/F 2.4
CL20 GAP GAP Azide 2.8
CL20 GAP DANPE 2.7
CL20 GAP BTTN / TMETN (80:20) 2.8
CL20 GAP BDNPA/F 2.7
5) 40g of CL20 was wetted to 25% moisture content with deionised water and
mixed thoroughly. 2g of TMETN (stabilised with 2% 2NDPA) was added
and again mixed thoroughly. The final CL20 / water I TMETN / 2NDPA mixture
was placed on the open bench to allow water evaporation and final water
was removed under vacuum storage at 80 C for 2 hours). Friction sensitiveness
assessment of the dry powder formed was carried out and an FofF = 2.4
determined.
