PRIORITY DOCUMENT

[0001 ] The present application claims priority from Australian Provisional Patent Application No.

2016900463 titled "PYROTECHNIC SHEET AND/OR METHOD OF PREPARING A

PYROTECHNIC SHEET" and filed on 1 1 February 2016, the content of which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

[0002 ] The present disclosure relates to cast and continuous pyro technic sheets and processes for preparing cast and continuous pyrotechnic sheets.

BACKGROUND

[00031 Pyrotechnic compositions comprising a mixture of at least one reducing agent, hereinafter also referred to as a fuel, and at least one oxidizing agent, hereinafter referred to as an oxidizer, are used in many applications such as civil, military and aerospace uses. For example, they can be used in fireworks, gas generators for vehicle airbags, infrared flares for military vehicles and igniters for rocket motors and ammunition.

[0004 ] Typically, energetic material compositions such as pyrotechnic compositions are supplied in granular form. However, they can also be provided in the form of a pyrotechnic or propellant solid bound with plastic binder. Such propellant or pyrotechnic plastic bound solids are disclosed in US 2,997,375, US 4,447,278, WO 90/1061 1 , WO 90/10724, GB 2269379 (A) and US 5,415,932.

10005] According to US 2,997,375, a propellant plastic bound solid, rubbery gel may be prepared by casting a fluid slurry comprising finely divided polyvinyl chloride, plasticizer for the polyvinyl chloride and finely divided ammonium perchlorate oxidizer into a mould, heating, and then cooling. The propellant plastic bound solid oxidizer that is prepared from this castable composition suffers from a number of drawbacks. The polyvinyl chloride must be dissolved in a plasticizer, but the plasticizer may act as a dilutant at a high proportion and the performance of the composition may be reduced accordingly. Notably, the ratio of polyvinyl chloride to plasticizer is desirably present in the ratio 2 parts to about 3 parts of plasticizer, and preferably in a ratio of 1 to 1. In addition, the mixing and castability of this composition may be problematic, and it is claimed in US 4,447,278 that as the polyvinylchloride is a thermoplastic it has never been actually possible to use the type of composition described in US

2,997,375. [0006] According to WO 90/1061 1 and WO 90/10724, a pyrotechnic sheet may be prepared by vapour deposition of at least one layer of an oxidizable metallic material on at least one portion of a side of an oxidizing polymeric film. The oxidizing polymeric film is preferably made of a halogenated polymer, and polytetrafluoroethylene (PTFE) is most preferred in terms of its potential energy content. It is also disclosed that the film thickness is preferably to be between 5 and 200 microns, more preferably between 10 and 100 microns, and the layer of an oxidizable metallic material is preferably from 3 to 100 microns thick, most preferably from 3 to 50 microns thick.

[0007] GB 2269379 (A) employs a porous, vapour-permeable oxidizing polymeric film instead of a solid oxidizing polymeric film for example used in WO 90/1061 1 and WO 90/10724 to enhance the burning rate of the pyrotechnic sheet made through vapour deposition.

[0008] However, the vapour deposition processes which have been used to prepare a pyrotechnic sheet are conventionally conducted in essentially oxygen free environments such as a vacuum or a low pressure inert atmosphere.

[0009] There is a need for processes that provide a pyrotechnic sheet that overcome or at least mitigate in part one or more of the disadvantages of known pyrotechnic sheets. Alternatively, or in addition, there is a need to cost effectively mass produce pyrotechnic sheets using a simpler method than vapour deposition.

SUMMARY

[0010] According to a first aspect, there is provided a process for preparing a pyrotechnic sheet, the process comprising:

- dissolving a polymer binder in a solvent to form a polymer binder solution;

- introducing one or more powdered oxidizers to the polymer binder solution to form a pyrotechnic loaded solution; and

- forming a sheet comprising particles of one or more oxidizers on a substrate by removing the solvent from the pyrotechnic loaded solution.

[001 1 ] In certain embodiments, the polymer binder serves as the fuel in the pyrotechnic loaded solution and the resultant pyrotechnic sheet.

[0012] In certain embodiments, one or more powdered fuels is introduced to the polymer binder solution in addition to the one or more powdered oxidizers to form the pyrotechnic loaded solution. [0013] Thus, according to a second aspect there is a provided a process for preparing a pyrotechnic sheet, the process comprising:

- dissolving a polymer binder in a solvent to form a polymer binder solution;

- introducing one or more powdered oxidizers and one or more powdered fuels to the polymer binder solution to form a pyrotechnic loaded solution; and

- forming a sheet comprising particles of one or more oxidizers and particles of one or more fuels on a substrate by removing the solvent from the pyrotechnic loaded solution.

[0014 ] According to a third aspect, there is provided a pyiOtechnic sheet formed according to the process of either the aspect or the second aspect.

[0015 ] According to a fourth aspect, there is provided a pyrotechnic sheet comprising a polymer binder, oxidizer particles and fuel particles, wherein the sheet has a thickness in the range of from about 0.1 mm to about 1.00 mm.

[0016] In certain embodiments of the third and fourth aspects, the pyrotechnic sheet comprises a plurality of layers. Within each layer, the heavier particles, usually the oxidizer, may be in the lower portion of each layer, however they are generally sufficiently intermixed with fuel particles to form a pyrotechnic mixture.

[0017] According to a fifth aspect, there is provided a pyrotechnic device which comprises at least one sheet of either the third aspect or the fourth aspect.

BRIEF DESCRIPTION OF DRAWINGS

[ 0018 ] Embodiments of the present invention will be discussed with reference to the accompanying drawings wherein:

[0019] Figure 1 is a schematic representation of a multilayer thermite pyrotechnic sheet in accordance with an embodiment of the present disclosure;

[0020] Figure 2 is a photograph showing letters produced from the multilayer thermite pyrotechnic sheet depicted in Figure 1;

[0021 ] Figure 3 is a photograph showing combustion of the multilayer thermite pyrotechnic sheet depicted in Figure 1 ; [0022 ] Figure 4 is a photograph showing combustion of pyrotechnic tape on a vertical surface; and

[ 0023] Figure 5 is a photograph showing combustion of Boron/Barium nitrate/Potassium perchlorate based pyrotechnic sheet.

DESCRIPTION OF EMBODIMENTS

[0024] Disclosed herein is a process for preparing a pyrotechnic sheet. The process comprises dissolving a polymer binder in a solvent to form a polymer binder solution. One or more powdered oxidizers is/are introduced to the polymer binder solution to form a pyrotechnic loaded solution. A sheet comprising particles of one or more oxidizers is then formed on a substrate by removing the solvent from the pyrotechnic loaded solution.

[ 0025] The polymer binder itself may serve as the fuel in the pyrotechnic loaded solution and the resultant pyrotechnic sheet. However, in practice, the use of polymer binders alone as a fuel tends to result in pyrotechnic sheets that have a slow bum rate. Whilst this may be suitable for some applications, it is generally preferred that a powdered fuel is also introduced to the polymer binder solution in addition to the one or more powdered oxidizers to form the pyrotechnic loaded solution. The combination of oxidizer with fuel is referred to as a pyrotechnic composition, and generally the oxidizer and fuel particles are mixed together before being introduced to the polymer binder solution. A sheet comprising particles of the oxidizer and fuel is then formed on the substrate by removing the solvent from the oxidizer and the fuel loaded solution. The oxidizer together with the fuel is present mixed together in a layer of the pyrotechnic sheet.

[0026] For ease of further discussion, reference will now generally be made to pyrotechnic loaded solution comprising the polymer binder, the powdered oxidizer and the powdered fuel. However, it will be appreciated that the following discussion also applies, where relevant, to embodiments of the invention in which the polymer binder is the fuel.

[0027] The process described provides pyrotechnic sheets that can be used in a number of ways that traditional pyrotechnics cannot. Furthermore, the process described herein may reduce safety hazards when working with sensitive pyrotechnics since no friction or pressing induced initiation mechanisms are employed to make the pyrotechnic.

[0028] The polymer binder used herein can be a polymer that can be readily dissolved in an organic solvent and form a sheet or film on a substrate after the solvent is removed. In certain embodiments, the polymer binder is a chlorinated polymer. The chlorinated polymer may contain about 57% by weight of chlorine. In this context, the polymer binder can be polyvinyl chloride (PVC). The PVC may have a weight average molecular weight of 100,000 to 200,000. Polyvinyl chloride can not only serve as a binder but also a fuel. A suitable PVC is commercially available from E.I. Dupont De Nemours & Company, Wilmington, Del. and is available in a number of grades and weights, including the 40W, 150W, 240W, 265W and 360W formulations, among others. Plasticisers may be present within the commercially available PVC.

[00291 Any solvent in which PVC dissolves can be used although it is preferred that the solvent be sufficiently volatile for the solvent to evaporate readily to form a film or sheet. In certain embodiments, the solvent is tetrahydrofuran (THF).

[0030 ] Another polymer binder that can be used is expanded polystyrene which can be dissolved in acetone, THF or chloroform provided that the combination provides a flexible relatively uniform film or sheet when the solvent evaporates.

[0031 1 Still another polymer binder that can be used is poly(vinyl alcohol) which can be dissolved in boiling water.

[00321 From the foregoing, it will be evident that a number of polymer/solvent combinations could be used and that the present disclosure is not intended to be limited to the aforesaid embodiments. The main criteria in choosing a polymer solvent combination are that the polymer dissolves in the solvent, the solvent is sufficiently volatile to allow evaporation with concomitant film/sheet formation, and upon solvent evaporation the polymer binder forms an intact sheet or film that is flexible and relatively unifonn in structure.

[0033] The solvent employed in the above method should be capable of dissolving the polymer binder and being readily removed under desirable film-forming conditions. The solvent should have a suitable evaporation rate so as to obtain an intact sheet. Generally, the solvent can include tetrahydrofuran, chloroform, toluene, acetone, and xylene. In the case of polyvinyl chloride, tetrahydrofuran can be used as the solvent.

[0034] The pyrotechnic mixture of oxidizer and fuel are selected to ensure reliable and consistent progression characteristics of the combustion properties. For example, hygroscopic lithium nitrate readily absorbs moisture from the atmosphere and the pyrotechnic sheet needs to be prepared under low humidity conditions and kept dry in a desiccator. In another example, increasing the weight percentage of boron fuel can be used to speed up the burn rate of the pyrotechnic sheet. The oxidizer can be selected from potassium perchlorate, potassium nitrate, potassium chlorate, barium nitrate, strontium nitrate, sodium nitrate, sodium perchlorate, lithium nitrate, ferric oxide, cupric oxide, ammonium perchlorate, and ammonium nitrate. [0035] The fuel can be selected from boron, aluminium powder, paint grade flake aluminium, silicon, magnesium, magnalium, iron, zinc, titanium, tungsten, copper, carbon e.g. graphene, zirconium, and alloys thereof. For instance, when polystyrene is used as the polymer binder, the oxidizer can be potassium perchlorate and the fuel can be silicon.

[0036 ] Specific combinations of oxidizer and fuels that can be used include potassium perchlorate with boron fuel, ammonium perchlorate with boron fuel, ammonium perchlorate with silicon fuel, potassium perchlorate and ferric oxide with boron fuel, ferric oxide with aluminium fuel, barium nitrate with magnesium fuel, barium nitrate and potassium perchlorate with boron fuel, barium nitrate and potassium chlorate with boron fuel, strontium nitrate with magnesium fuel, sodium nitrate with magnesium fuel, potassium perchlorate with titanium fuel, potassium perchlorate with carbon fuel, and potassium chlorate with silicon fuel.

[0037] In certain embodiments, a mixture of silicon and/or boron fuel, and potassium perchlorate oxidizer can be employed in the pyrotechnic composition.

[0038 ] Different combinations of oxidizers and fuels can be used to produce varying effects, in particular fast and slow burn rates by changing the oxidizer to fuel ratio, colours such as yellow (sodium nitrate), green (barium nitrate, or boron), and red (strontium nitrate), and sparks from titanium fuel.

[0039] The amount of oxidizer is desirably sufficient to oxidize at least some of the fuel present in the pyrotechnic sheet. However, for some uses, such complete oxidation is not necessary as oxygen from air may participate in the reaction and the proportion of oxidizer may be reduced under these conditions. The amount of the polymer binder should not prevent effective combustion of the pyrotechnic sheet.

Generally, the polymer binder comprises from about 7% to about 37% by weight of the pyrotechnic sheet, the oxidizer comprises from about 40% to about 70% by weight of the pyrotechnic sheet, and if present, the fuel comprises from about 10% to about 40% by weight of the pyrotechnic sheet.

[0040] The particle size of the powdered oxidizer and the powdered fuel may affect not only their dispersion in the polymer binder solution but also the ignition and combustion properties of the pyrotechnic sheet. Thus, the particle size of powdered oxidizer and the powdered fuel should usually be in the range of 0.5 micrometres to 500 micrometres, with a typical size about 125 micrometres. If the particle size is too large the oxidizer will not mix well with the fuel and may not support combustion. If the particle size is too small, the oxidizer and fuel may become too reactive and therefore more sensitive to unplanned ignition and therefore more hazardous. However, depending upon the properties of the particular oxidizer and fuel it may be possible to employ particles smaller than 0.5 micrometres. [0041 ] Before forming a sheet on the substrate, it is preferable to evenly disperse the powdered oxidizer and the powdered fuel in the polymer binder solution by a suitable method, such as sieve mixing the oxidizer and fuel into the solution.

[0042 ] It will be appreciated by the skilled person in the art that additives including, but not limited to, plasticizers, stabilizers, release agents, colorants, pigments, etc. can be present in order to stabilize the shelf life of the pyrotechnic sheet, or modulate the properties of the pyrotechnic sheet, such as burn-rate, burn temperature, infrared spectral output or optical colour of combustion.

[0043 ] Explosives and/or other energetic materials can also be used as additives in the pyrotechnic sheet. For example, the high explosive RDX may be incorporated into the pyrotechnic sheet and may complement the properties of the sheet.

[0044 ] To obtain an intact and continuous sheet, the solid components (such as the polymer binder, the powdered oxidizer, and the powdered fuel) comprise from about 5% to about 20% by weight of the pyrotechnic loaded solution.

[00451 The substrate also plays a role in achieving an intact and continuous sheet. It will be appreciated by the skilled person in the art that any substrate that allows the sheet to be released from it without substantially damaging the sheet can be used. Generally, it can be glass plate, stainless steel, PTFE, ceramic, or similar non-reactive substrate.

[0046] The solvent can be removed from the pyrotechnic loaded solution under any temperature/pressure conditions that result in evaporation of the solvent under conditions to form a polymer film or sheet. For example, the polymer solution may be air dried, or dried under a flow of diy nitrogen gas. Other film forming technologies known in the art could also be used.

[0047 J In the present process the polymer binder is dissolved in a solvent with a high ratio of binder to solvent, e.g. 1 g of polyvinyl alcohol to 50 ml of tetrahydrofuran, approximately 1 part binder to 50 parts solvent. Following the addition of pyrotechnic composition, the solvent is permitted to evaporate. The solvent therefore does not act as a diluent. In addition, a very wide range of oxidizers and fuels may be employed in the pyrotechnic composition described herein, improving ignition and combustion properties of the pyrotechnic sheet. Furthennore the pyrotechnic sheet described herein may have multiple layers of pyrotechnic composition within the sheet, enabling ignition of pyrotechnic compositions that may otherwise be difficult to ignite.

[0048 ] The thickness of the continuous pyrotechnic sheet can be adjusted in the light of practical uses by altering either the amount of polymer binder dissolved in solution, or the amount of pyrotechnic mixture deposited, e.g. by sieve mixing, into the polymer solution. The thickness is usually within the range of from about 0.1 to about 1.0 mm.

[0049] It is often observed that the oxidizer together with the fuel may be present in the polymer sheet with the heavier oxidizer particles closer to the bottom of the thin layer sheet, and the lighter fuel particles at the top. It may be possible to adjust this distribution by allowing more evaporation of the solvent from the solution. As the viscosity of the solution increases there is less separation of the oxidizer particles and the fuel particles.

[0050 ] The process can be used to form a single layer sheet or a multilayer laminate. In the latter case, the solvent/polymer mixture is allowed to partially dry or thicken before the second step is repeated using a further lot of oxidizer and fuel (which may be the same or different to the first lot of oxidizer and fuel). This process can be repeated to build up layers having different oxidizer/fuel compositions in each layer.

[0051 1 As used herein, the term "layer" and variants thereof is intended to include within its scope discrete layers with defined compositional boundaries between adjacent layers, as well as layers having compositional gradients between adjacent layers.

[0052 ] Alternatively, a multilayer laminate sheet comprising at least one layer comprising the oxidizer and the fuel and at least one layer comprising a primer for the particular oxidizer/fuel combination used. Alternatively, or in addition, the multilayer sheet may comprise at least one layer comprising the oxidizer and the fuel and at least one layer comprising an ignition primer. The primer and/or ignition primer layers in these embodiments assist in igniting the fuel and oxidizer combination and this may be particularly suitable for fuel/oxidizer combinations that are difficult to ignite. For example, the oxidizer/fuel combination may be thermite, an adjacent layer may comprise a thermite and an outermost layer (adjacent the thermite primer layer) may comprise an ignition primer (Figure 1 ). After each deposition of pyrotechnic mixture, the solvent is permitted to evaporate, and a new layer then applied, building up discrete layers. By employing this approach a very fast burning ignition primer layer, e.g. potassium perchlorate / boron (70 : 30), may be deposited first into solution, followed by a slower burning priming layer e.g. potassium perchlorate, ferric oxide, and boron, followed by a slow burning hard to ignite thermite composition based on ferric oxide and aluminium. This may be followed by an additional thermite layer, and additional thermite priming layer, and finally a very fast burning ignition layer. Such morphology or structure can provide versatile ignition transfer from one layer to the next. To improve ignitability, both sides of the pyrotechnic sheet can be coated with very fast burning pyrotechnic composition. Thus, in certain embodiments, at least one surface of the pyrotechnic sheet comprises an ignition sensitive primer. [0053] Advantageously, the pyrotechnic sheet can produce different optical colours. A single pyrotechnic sheet, consisting of one layer pyrotechnic composition, may have a barium nitrate based pyrotechnic composition in half the sheet, and a strontium nitrate based composition in the other half of the sheet. Ignition of the pyrotechnic sheet at one end may then produce green coloured combustion, followed by red coloured combustion. Similar effects may be produced in the infrared region of the electro-optical spectrum depending upon the fuels employed in the pyrotechnic sheet.

[0054 ] The pyrotechnic sheet can be attached to an adhesive, such as double sided tape, to provide an ignition fuse for vertical surfaces (see e.g. Figure 4). The pyrotechnic sheets of these embodiments can be packaged in a roll, like masking tape, for military applications such as fusing or signalling.

[0055] Multilayer deposition can produce double sided (top and bottom) priming ignition for micro- structured six layer thermite based sheets. With a total sheet thickness of about 0.6 mm (Figure 1 ), shapes may be cut from the pyrotechnic sheets thus produced and then ignited to produce a pyrotechnic glow that can be maintained for shapes, letters and words for several seconds (Figure 2).

[0056] Flakes formed from the pyrotechnic sheet can be uniformly ignited and dispersed and propelled from a suitable flare tube.

[0057] The pyrotechnic sheet may be employed as a carrier for ignition of special effects, e.g. sparks from titanium combustion or explosive materials such as RDX. The length of flakes cut from the pyrotechnic sheet is versatile, therefore quick burning or slow burning flakes can be produced depending upon the length of the flakes.

[0058] Another important aspect is control of ignition and ignition transfer between internal layers in pyrotechnic sheet. Ignition priming with potassium perchlorate / boron composition, and multilayer formation of pyrotechnic sheets result in a product that is easier to ignite.

[0059] In one embodiment pyrotechnic sheet can be employed in indoor celebrations, e.g. as with sparklers, but the cut shapes from pyrotechnic sheet may upon ignition display numbers, names or sentences as glowing letters.

[0060] In another embodiment pyrotechnic sheet may be employed as bunches of flakes in aerial firework displays covering large areas of the sky with glowing flakes, or with traces of smoke depending upon the composition.

10061 ] In another embodiment, the manufacture of pyrotechnic sheet is a technique of additive manufacturing which may be used to produce pyrotechnic objects of specified shape, dependent upon the shape of the structure the polymer solution has been placed in. The technique employed in the preparation of pyrotechnic sheet may be employed in 3D printing of pyrotechnics.

[0062] It will be evident from the foregoing discussion that provided herein, in a second aspect, is a process for preparing a pyrotechnic sheet. The process comprises dissolving a polymer binder in a solvent to fonn a polymer binder solution. One or more powdered oxidizers and one or more powdered fuels are then introduced to the polymer binder solution to fon a pyrotechnic loaded solution. A sheet comprising particles of one or more oxidizers and particles of one or more fuels is then fonned on a substrate by removing the solvent from the pyrotechnic loaded solution.

[00631 According to a third aspect, there is provided a pyrotechnic sheet formed according to the process as described herein.

[0064 ] According to a fourth aspect, there is provided a pyrotechnic sheet comprising a polymer binder, oxidizer particles and fuel particles, wherein the sheet has a thickness in the range from about 0.1 mm to about 1.00 mm.

[00651 According to a fifth aspect, there is provided a pyrotechnic device which comprises at least one sheet of either the third aspect or the fourth aspect.

EXAMPLES

[0066] Embodiments of the present disclosure are further described in the following non-limiting examples.

[0067] Preparation of a pyrotechnic sheet

[0068] A pyrotechnic sheet was prepared by sieve mixing an oxidizer with a fuel through a small #52 sieve, and sieving the mixture, usually about 2 g, onto the surface of a beaker (e.g. 600 cm ³ ) of a solution of 1.00 g polyv inyl chloride (PVC) dissolved in 50 cm ³ of warm (50 °C) tetrahydrofuran (THF), and allowing the solution to dry. A beaker of hot water was used to dissolve the PVC in the THF. A common ratio of oxidizer/fuel/PVC is 1 : 1 : 1 , i.e. 1 g of each is used. Additional pyrotechnic compositions can be sieved into the same beaker, enabling layers of pyrotechnics to be produced.

[0069] Chemicals used include potassium perchlorate (KCIO4) blended mix of 38 μηι and 63 μιη particles, barium nitrate (Ajax, Unilab LR), strontium nitrate (Ajax, Univar AR), sodium nitrate (BDH AR), fenic oxide, cupric oxide, aluminium powder or dried aluminium paste (S I 6), boron (Trona), silicon, magnesium (Gr. 5 cut), copper powder. All oxidizers and fuels were dried prior to use, and the solution of pyrotechnic composition was left undisturbed while the solvent evaporates in a fume hood overnight. The side of the dried polymer film was pulled away from the side of the beaker using a wooden stick, and the resultant sheet removed.

[0070 ] Combustion of flakes of the pyrotechnic sheet was generally undertaken on 5 cm x 1 cm flakes suspended from a small bulldog clip hanging on a wire (see e.g. Figure 5). A pyrotechnic match on the end of a wooden wand was used for ignition, or alternatively electrical initiation with an electric matchhead. The burn time of the flake was timed, and photos or videos recorded of the combustion.

[0071 ] Results

[0072] Pyrotechnic sheet has been prepared with many combinations of oxidizer and fuel. Generally burn tests were undertaken on strips cut from pyrotechnic sheet ("PyroFilm") measuring 5 cm long and 1 cm wide. Three gram pyrotechnic sheets were prepared containing 1.55 g potassium perchlorate and 0.45 g boron, deposited with sieve mixing in a polyvinyl chloride (PVC) solution containing 1.00 g of PVC dissolved in 50 ml of tetrahydrofuran (THF). The final mass of the pyrotechnic sheet was 3. 10 g, with a burn time of 2.3 s. When the proportion of boron was increased to 30% by weight, the burn time was about 1.0 s.

[0073 ] A pyrotechnic composition consisting of 1.00 g of potassium perchlorate was mixed with 0.50 g of strontium nitrate and 0.50 g of magnesium (Grade 5 cut). The pyrotechnic composition was then sieve mixed into a beaker containing 1.00 g of PVC dissolved in THF. A second pyrotechnic composition consisting of 0.1 1 g of potassium perchlorate was mixed with 0.10 g of boron and sieve mixed on top of the PVC solution containing the first composition. The solvent was permitted to evaporate and the pyrotechnic sheet weighed at 3.21 g. A 5 cm by 1 cm flake was cut from the sheet and on burning an intense red flame was observed with a burn time of 4.8 s.

[0074] Pyrotechnic lettering

[0075] When the pyrotechnic sheet forms, the bottom layer contains the pyrotechnic mixture as it sinks to the bottom of the PVC/THF solution, while the top layer is mostly polymer. To coat both the top as well as the bottom layer, partial drying of the PVC/THF solution is required. As the solution thickens, another pyrotechnic layer may be sieved on the top. In this way an ignition priming layer may be deposited first, followed by the principal or main composition, and a priming layer deposited on the top as well. The main composition is then sandwiched between the two ignition priming layers, facilitating ignition. When thermite pyrotechnic sheet is made, an extra layer is required in-between the ignition primer and the main aluminium/iron oxide thermite composition. This extra layer is referred to as a thermite primer and it is required to ensure ignition of the difficult to ignite thermite mixture. To produce a double sided thermite based pyrotechnic sheet, a total of six layers are produced, with a total thickness of about 0.6 mm, as shown in Figure 1.

[0076] Normally, a pyrotechnic only produces flame from the ignited surface, and as this surface is combusted the flame front propagates downwards or upwards long its bum path. One of the benefits of using a thermite pyrotechnic sheet as described herein is that the whole of the pyrotechnic composition can be made to glow for several seconds. This is shown in Figure 3.

[0077 ] Letters can be produced using thermite based pyiOtechnic sheet by cutting the shape of the letters from a pyrotechnic sheet and igniting the pyrotechnic sheet, as shown in Figure 2. The glow from the pyrotechnic combustion allows the letters to be read for several seconds.

[0078] Other end user applications

[0079] The pyrotechnic sheet can be placed on double sided tape and this allows the sheet to be easily attached to any flat surface, whether upside down or vertical. A demonstration of this is shown in Figure 4. The pyrotechnic sheet may consist of a roll of tape which is sticky on one side, and is as easy to apply as masking tape, an advantage over plastic igniter cord (PIC). PIC is not able to be employed attached to surfaces except through the use of masking tape to hold the PIC in position. Different special effects may also be produced from pyrotechnic sheet, making it much more versatile than PIC.

[0080] Variations

[0081 ] Pyrotechnic sheets of 16cm diameter were produced with boron/carbon graphene/potassium perchlorate (2.04 g: 0. 14g: 4.62g), in PVC (3.2 g)/THF ( 158 cm?), making a total pyrotechnic sheet mass of 10 g.

[0082] A number of other compositions were also prepared and studied as pyrotechnic sheets. This includes the use of ammonium perchlorate (AP, HD Class 1.1 explosive), cyclotrimethyltrinitramine (RDX) explosive, and potassium chlorate oxidizer. These compositions have been previously prepared as pressed or extruded pyrotechnic grains, but their manufacture as thin pyrotechnic sheets / films for the first time may result in new applications.

[ 0083] In addition, pyrotechnic sheets can be deposited in other shapes, in particular in narrow channels and in rectangular shapes. It was observed that the PVC/THF solution has a significant surface tension in narrow channels of a polyethylene container, resulting in less PVC deposited on the bottom of each channel and more on the sides of each channel. This resulted in a much more fragile film at the bottom. However, in other polyethylene containers, good polymer films could be formed. [0084 ] A comparison was made between different coloured light emission from pyrotechnic sheets employing potassium perchlorate (KCIO4) compared to potassium chlorate (KClCb) to produce green flame. It was observed that the potassium perchlorate based pyrotechnic sheets produced a better greener emission from combustion of the 5 cm x 1 cm rectangular 0.5 g flakes (Figure 5). The degree to which the flame appears green is known to be correlated with the formation of boron dioxide radical, and this appears favoured with potassium perchlorate.

[0085 ] Throughout the specification and the claims that follow, unless the context requires otherwise, the words "comprise" and "include" and variations such as "comprising" and "including" will be understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any other integer or group of integers.

[0086 ] The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement of any form of suggestion that such prior art forms part of the common general knowledge.

[0087] It will be appreciated by those skilled in the art that the invention is not restricted in its use to the particular application described. Neither is the present invention restricted in its preferred embodiment with regard to the particular elements and/or features described or depicted herein. It will be appreciated that the invention is not limited to the embodiment or embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the scope of the invention as set forth and defined by the following claims.