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Patent application title: rapid gas generating pyrotechnical composition and method for obtaining same

Inventors: frederic marlin

agents: hamre, schumann, mueller & larson, p.c.

assignees: snpe materiaux energetiques

origin: minneapolis, mn us

ipc8 class: ac06b3100fi

uspc class: 149 45

patent application number: 20090308509

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Abstract:

The subject-matter of the present invention is: pyrotechnic compositions generating gases, whereof at least 95% by mass of the charges are constituted by constitutive ingredients hereinbelow: a reducing charge in the form of at least

one organic nitrogen compound; an oxidizing charge in the form of at least one basic metal nitrate; and less than 30% by mass of a second oxidizing charge in the form of at least one alkaline metal perchlorate; andwhich are obtained

via a dry roller compacting step of a pulverulent mixture essentially constituted by said powder ingredients; and also the method for obtaining such compositions. The compositions of the invention have interesting combustion speeds.

Claims:

1. A pyrotechnic composition generating gases, whereof at least 95% by mass of the charges are constituted by the constitutive ingredients hereinbelow:a reducing charge in the fo rm of at least one organic nitrogen compound;an

oxidizing charge in the form of at least one basic metal nitrate; andless than 30% by mass of a second oxidizing charge in the form of at least one alkaline metal perchlorate; andwhich is obtained via a dry r oller compacting step of a

pulverulent mixture essentially constituted by said powder ingredients.

2. The composition according to claim 1, in the form of shaped objects, granules, pellets or extruded monolithic blocks.

3. The composition according to claim 1, wherein that said at least one or ganic nitrogen compound is selected from guanidine nitrate, nitroguanidine, guanyl urea dinitramide and their mixtures; in that said at l east one organic nitrogen

compound consists advantageously of guanidine nitrate.

4. The composition according to claim 1, wherein that said at least one basic m etal nitrate is selected from basic copper nitrate, basic zinc nitrate, basic bismuth nitrate and their mixtures; i n that said at least o ne basic metal nitrate

consists advantageously of basic copper nitrate.

5. The composition according to claim 1, wherein that said at least one al kaline metal perchlorate is selected from potassium perchlorate, sodium perchlorate and their mixtures; in that said at l east one alkaline metal perchlorate


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consists advantageously of potassium perchlorate.

6. The composition according to claim 1, wherein that said at least one or ganic nitrogen compound is present at a rate of 4 5 to 65% by mass.

7. The composition according to claim 1, wherein that said at least one basic m etal nitrate is present at t he rate of 15 to 35% by mass.

8. The composition according to claim 1, wherein that said at least one al kaline metal perchlorate is present at the rate of 10 to 25% by mass.

9. The composition according to claim 1, wherein that it is i n the form of extruded monolithic blocks and in that said blocks include up to 10 % by mass of a dry gel.

10. The composition according to claim 9, w herein that said gel is selected from cellul osic gels, gels obtained from acrylic elastomers, ethylene-vinyl-acetate copolymers with high acetate rate, polyester polymers and their mixtures.

11. The composition according to claim 9, w herein that said gel is sodium carboxymethyl cellulose gel.

12. A method for obtaining a pyrotechnic composition generating gases, wherein it comprises:dry mixing of powders consisting for at least 95% by mass of a pulverulent reducing charge in the fo rm of at least one organic nitrogen

compound, a pulverulent oxidizing charge in the form of at least one basic metal nitrate and less than 30% by mass of a second oxidizing pulverulent charge in the form of at least one alkaline metal perchlorate; anddry roller

compacting of the resulting mixture of powders.

13. The method according to claim 12 , wherein that said powders have granulometry less than or equal to 4 0 .mu.m.

14. The method according to claim 12 , wherein that it furt her comprises dry granulation of the compacted mixture of powders for generating granules.

15. The method according to claim 14 , wherein that it furt her comprises pelleting of said granules.

16. The method according to claim 14 , wherein that it furt her comprises mixing said granules with a gel and extruding said gel loaded with s aid granules.

17. The method according to claim 12 , wherein that it comprises recycling fines generated during the dry compacting phase and/or during the granulation phase.

18. The method according to claim 14, wherein that it comprises recycling fines generated during the granulation process.

Description:

[0001]the present invention relates to pyrotechnic gas generation, especially for inflating cushions used in systems for protecting occupants of an automobile. The present invention more pr ecisely relates to pyrotechnic compositions

known as cold pyrotechnic compositions rapidly generating clean and non-toxic gases at temperatures acceptable for automobile safety (temperatures qualified as low, that is, under 2200 k). The present invention also relates to a

method for producing such pyrotechnic compositions.

[0002]within the scope of automobile safety, the pyrotechnic compositions employed in gas generators must provided the quantity of g as necessary for putting in place the inflatable cushion in an extremely short time, typically

between 10 and 40 milliseconds. Also, the gases generated must be clean, that is exempt from solid particles (likely to constitute hot points which might damage the wall of said cushion) and non-toxic, that is having low content of

carbon monoxide, nitrogen oxides and chlorinated products.

[0003]various types of pyrotechnic compositions have already been proposed to date.

[0004]currently, those pyrotechnic compositions appearing to offer the best compromise in terms of gas temperature, gas yield, rate of particles emitted and toxicity contain, as principal i ngredients, guanidine nitrate (gn) and basic

copper nitrate (bcn). U.s. pat. No. 5,608,183 describes such compositions, obtained by wet method.

[0005]these compositions do however have the disadvantage of having relatively slow combustion speeds, less than or equal to 20 mm/s at 20 mpa and being difficult to ignite. Similarly, they are very diffi cult to use i n hybrid and side

generators which need very brief operating time, between 10 and 20 mill iseconds.

[0006]it has been proposed, according to the prior art, to add perchlorates to such pyrotechnic compositions based on guanidine nitrate (gn) and basic copper nitrate ( bcn): [0007]in patent application ep 1 526 121, t he addition of

perchlorate is described (especially potassium perchlorate), at a low rate (less than 5% by mass), to improve ignition of said compositions and decrease emission of nitrogen oxides; [0008]in u.s. pat. No. 6,89 3,517, the addition of

perchlorate is described (especially potassium perchlorate), at relatively high rates (between 30 and 45% by mass), to boost the combustion speed of said compositions. Such rates of perchlorate cause high combustion temperatures, of

around 2400 k. The p yrotechnic compositions in question can no longer be considered as cold, with r espect to the non-aggression of inflatable cushions by the combustion gases.

[0009]in reference to the technical problem of a speed increase in combustion of pyrotechnic compositions based on guanidine nitrate (gn) and basic copper nitrate (bcn), t he addition of perchlorate is therefore not a satisfactory

solution per se.


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[0010]the roller compacting and dry granulation method is also known, implemented in different contexts, for t reating powders, generally mixtures of powders. Such mixtures of powders, coming from a dry powder mixer, are

transported, for example by a metering screw, to supply a c ylinder compacter. Such a compacter is composed of two rotating cylinders, placed in rotation at a defined speed, in the opposite direction. The powder mixture is pushed by

the metering screw between said two cylinders. A known effort is applied to the cylinders. Accordingly, the material passing between them, at a given rate, is compacted in the form of a flat plate. Such an operation places a strong rate

of compression and shearing on the mixture which improves the closeness between the constituents. The compacted product, originating from the compacter is t hen broken and forced through a grater to generate granules. Such

granules generally turn out t o be easier to handle than the starting powders. A single device generally successively manages both compacting and granulation.

[0011]within the scope of the present invention, the inventor has shown, in reference to the technical problem of the increase in combustion speed, that the major interest is to carry out dr y roller compacting in the context of the

making of pyrotechnic compositions of guanidine nitrate and basic copper nitrate t ype. A real synergy has surprisingly been observed: the positive effect (on the combustion speed) due to intervention of a limited quantity of

perchlorate (without harmful effect on the combustion temperature) is potentialised by carrying out dry roller compacting; use of which has per se no substantial effect in the absence of perchlorate. In support of this affirmation,

comparative data hereinbelow can be supplied on combustion speeds at 20 mpa:

[0012]gn+bcn.ltoreq.20 mm/s

[0013]gn+bcn+compacting 20-22 mm/s

[0014]gn+bcn+kclo.sub.4 (example 4 hereinbelow) 32 mm/s

[0015]gn+bcn+kclo.sub.4+compacting (example 5 hereinbelow) 38.2 mm/s.

[0016]according to its fir st object, the present invention therefore relates t o pyrotechnic compositions generating gases which combine two characteristics. Said pyrotechnic gas compositions: [0017]include, as principal constitutive

(active) ingredients: [0018]a reducing charge in the form of at least one organic nitrogen compound; [0019]an oxidizing charge in the form of at least one basic metal nitrate; and [0020]less than 30% by mass of a second oxidizing

charge in the form of at least one alkaline metal perchlorate,

[0021]said charges representing at least 95% by mass (generally at least 98 by mass) of the charges present; and [0022]are obtained via a dry roller compacting step of a pulverulent mixture essentially made up of said powder

ingredients.

[0023]the pyrotechnic compositions of t he invention, including a specific reducing charge (in the form of at l east one organic nitrogen compound) and a specific oxidizing charge (in the form of at least one basic metal nitr ate), include

a limited quantity of a s pecific second oxidizing charge (in the form of at least one alkaline metal perchlorate) and are obtained on completion of a method including a dry roller compacting step of the pulverulent mixture including

said specific reducing and oxidizing charges.

[0024]dry roller compacting is carried out, as known per se, in a cylinder compacter, generally at a compacting pressure of between 10.sup.8 and 6.10.sup.8 pa.

[0025]the method for producing the pyrotechnic compositions of the invention which characteristically includes a dry roller compacting step, is described in detail further on i n the present text.

[0026]it can be carried out according to different variants (wit h a characteristic step of "simple" roll er compacting followed by at least one additional step, with a characteristic step of roller compacting coupled with a forming step . . .

) and the pyrotechnic compositions of the invention therefore exist in different forms.

[0027]in fact: [0028]on completion of the dry roller compacting coupled with forming (by using at least one compacting cylinder, whereof the external surface has alveoli), plates with relief patterns are obtained which can be broken

to directly obtain shaped pyrotechnic objects; [0029]on completion of dry roller compacting followed by granulation, granules are obtained; [0030]on completion of dry roller compacting followed by granulation then pelleting (dry

compression), pellets are obtained; [0031]on completion of dry roller compacting followed by granulation and then mixing the granules obtained with an extrudable binder and extrusion o f said binder loaded with said granules,

extruded monolithic blocks are obtained (loaded with said granules).

[0032]the pyrotechnic compositions of t he invention are therefore likely to exist in the form of: [0033]shaped objects, originating directly from roller compacting (coupled with forming); [0034]granules;[0035]pellets;

and [0036]extruded monolithic blocks (loaded with granules).

[0037]in a non-limiting manner it can be in dicated here that: [0038]granules according to the invention generally present granulometry (median diameter) of between 200 and 800 .mu.m (as well as apparent volumic mass between 0.8

and 1.2 cm.sup.3/g); [0039]pellets according to the invention generally have a thickness between 1 and 3 mm; and[0040]within the extruded monolithic blocks there are granules in a dry binder (gel).

[0041]it can also be pointed out here that the followings especially form part of t he first object of the i nvention: [0042]pellets whereof the combustion temperature is under 2200 k, the combustion speed at 20 mpa is greater than 30

mm/s and the oxygen balance between -2 and -4%; [0043]extruded monolithic blocks whereof the combustion temperature is under 2200 k, t he combustion speed at 20 mpa is greater than 24 mm/s and the oxygen balance between -2

and -4%.

[0044]it is now proposed to give some precise details, non-limiting, on t he ingredients making up the pyrotechnic compositions of the invention and their occurrence rate within said compositions.


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[0045]the at least one organic nitrogen compound, making up the re ducing charge, can especially be selected from guanidine nitrate, nitroguanidine, guanyl urea dinitramide and t heir mixtures. It consists advantageously of guanidine

nitrate (gn).

[0046]the at least one basic metal nitrate, constitutive of the (first) oxidizing charge can especially be selected from basic copper nitrate, basic zinc nitrate, b asic bismuth nitrate and their mixtures. It consists advantageously of basic

copper nitrate (bcn).

[0047]the at least one alkaline metal perchlorate can especially be selected fro m potassium perchlorate, sodium perchlorate and their mixtures. It consists advantageously of potassium perchlorate (kclo.sub.4).

[0048]according to a preferred variant, the principal constitutive ingredients of the compositions of the invention are therefore: [0049]guanidine nitrate (gn) [0050]basic copper nitr ate (bcn) and [0051]potassium perchlorate

(kclo.sub.4).

[0052]with respect to the respective quantities of each of said ingredients, there is generally, independently and advantageously in combination: [0053]said at least one organic nitrogen compound present at the rate of 45 to 65% by

mass; [0054]said at least one basic metal nitrate present at t he rate of 15 t o 35% by mass; [0055]said at least one alkaline metal perchlorate (as already indicated, present at less than 30% by mass. Its beneficial action on combustion

speed thus expresses, with potentialisation because of the compacting method, appreciably and t his without consequential and harmful elevation of combustion temperature) present at the rate of 10 to 25% by mass, advantageously

from 10 to 20% by mass.

[0056]according to a preferred variant, the pyrotechnic compositions of the invention include: [0057]from 45 to 65% by mass of guanidine nitrate (gn), [0058]from 15 to 35% by mass of basic copper nitrate (b cn), [0059]from 10 to

25% by mass of potassium perchlorate (kclo.sub.4).

[0060]the pyrotechnic compositions of t he invention, in the form of shaped objects, granules and pellets, consist essentially (at least at 9 5% by mass, generally at least at 98 % by mass), even exclusively (at 100% by mass), of the

principal constitutive ingredients (charges) identified hereinabove: said at least one organic nitrogen compound, said at least one basic metal nitrate and said at least one alkaline metal perchlorate. Said ingredients can in f act

themselves constitute at 100% the charges of said pyrotechnic compositions (this is generally the case), or even constitute said pyrotechnic compositions at 100%. However, the presence, within the compositions of the invention, of

other charges in minimal quantities could not be excluded (in any case, the charges identified hereinabove represent at least 95% by mass, generally at least 98% by mass of charges present) and/or that of at least one additive

(fabrication auxiliary type).

[0061]the pyrotechnic compositions of t he invention, in the form of extruded monolithic blocks, include those principal constitutive ingredients (charges) identified hereinabove (plus possibly, other charges in minimal quantities) in a

dry gel. This gel, extrudable per se or mixed with a solvent, entered upstream to allow extrusion. It occurs in an efficient qu antity (to allow extrusion), though limited so as not to substantially affect the performances of the

compositions of the invention.

[0062]the extruded monolithic blocks of the invention generally include no more than 10% by mass of such a dry gel. They advantageously include from 4 to 6% by mass. In their midst, t he synergy of the invention develops with the

same intensity.

[0063]the presence of at least one additive is also not excluded from this context. The principal constitutive ingredients (charges) and dry gel generally represent at least 95% by mass, very generally at least 98% by mass (or even

100% by mass) of said compositions.

[0064]with respect to the nature of said gel, it is not per se original. Said gel is generally selected from cellulosic gels, gels obtained from acrylic elastomers, ethylene-vinyl-acetate copolymers with a high acetate rate (including over

60% by mass of acetate units), polyester polymers, and their mixtures. Said gel advantageously consists of a sodium carboxymethyl cellulose gel.

[0065]according to its second object, the present invention relates to the met hod for obtaining p yrotechnic compositions such as d escribed hereinabove; a m ethod which characteristically comprises dry compacting of powders.

[0066]said method actually comprises: [0067]dry mixing of powders (charges) consisting for at least 95% by mass of a pulverulent reducing charge in the form of at least one organic nitrogen compound, a pulverulent oxidizing

charge in the form of at least one basic metal nitrate and less t han 30% by mass of a second pulverulent oxidizing charge in the form of at least one alkaline metal perchlorate; and [0068]dry roller compacting of the resulting mixture

of powders.

[0069]precise details on the nature o f the ingredients in question and their rate o f respective presence are specified hereinabove in the present text.

[0070]the ingredients making up the desired pyrotechnic compositions occur in the powdered state. Advantageously, said powders have fine granulometry, less than or equal to 40 .mu.m. Said granulometry (value of the median

diameter) is generally between 3 and 40 .mu.m.

[0071]the steps for dry mixing of the powders and dry roller compacting of the mixture obtained are executed conventionally. With respect to dr y roller compacting, it has been explained that it is carried out by passing the mixture of

the powders between two cylinders, the pressure exerted being generally between 10.sup.8 and 6.10.sup.8 pa. "simple" compacting with two cylinders having non-machined external surfaces or compacting coupled with forming wi th

cylinders, whereof the external surface of at least one of the two is machined to present alveoli, is carried out.

[0072]it is incidentally noted here that the o riginality of the invention as claimed is not based on the originality per se of t he method in question, but rather the or iginality of the execution of said method with particular mixtures of

powders.


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[0073]the method of the invention can be limited to these two successive steps of mixing and dry roller compacting, in the context hereinbelow: that of directly obtaining shaped objects, in the hypothesis of carrying out roller

compacting coupled with forming (the external surface of at least one of the compacting cylinders presenting alveoli).

[0074]the method of the invention, in addition to said two mixing and ("simple") dry roller compacting steps, can include:

[0075]a) a dry granulation step (the compacted mixture of powders is forced mechanically by a rotor via a grater acting as a screen whereof the mesh generally varies from 500 .mu.m to 3 mm). Roller compacting and granulation can

be carried out inside a single device or in two independent devices. The resulting pyrotechnic compositions are then in the form of granules (see above);

[0076]b) a dry granulation step (see above) followed by pelleting (dry compression during which the granules undergo pressure generally of between 4.10.sup.8 and 10.sup.9 pa. It is incidentally noted here that feeding the pelleting

mould impressions is much more easily carried out with granules than with starting powders). The resulting pyrotechnic compositions are thus in the form of pellets (see above);

[0077]c) a dry granulation step (see above) followed by mixing the granules obtained with an extrudable binder and extrusion o f said mixture. The pyrotechnic compositions finally obtained are in the form of extruded monolithic

blocks loaded with granules.

[0078]the variants of the method of the i nvention which include steps b) and c) hereinabove are particularly preferred. Within the scope of said two variants, the method of the invention includes the steps of ("simple") roller

compacting and dry granulation of the mixture of the starting powders.

[0079]irrespective of the exact variant of execution of the method of the invention, it has proven opportune, especially in reference to increasing the combustion speed of the prepared pyrotechnic composition, to recycle at least in part

the fines generated at the compacting step and/or at that of granulation, when said granulation step is carried out. Carrying out a fines recycling rate of between 10 and 30% i s specified.

[0080]the invention will now be illustrated, in no way limiting, by the examples hereinbelow. More precisely, examples illustrating two variants of the invention (pyrotechnic compositions in the form of pellets (example 5) and

extruded monolithic blocks (example 7)), are proposed, to be considered in parallel with comparative examples.

[0081]the powders (raw materials) utilised have fine granulometry: a median diameter of arou nd 20 .mu.m for kclo.sub.4, 4.5 .mu.m f or bcn, 10 .mu.m for gn.

[0082]such powders do not flo w and cannot therefore per se be used in i ndustrial pelleting (it is very diffi cult to fi ll the pelleting mould impressions).

[0083]table i hereinbelow shows formulation examples as well as the thermodynamic and ballistic performances of pellets (of around 2 mm in thickness) obtained by pelleting (performed at 5.10.sup.8 pa) of the powder mixtures not

pre-compacted.

Table-us-00001 table i (direct pelleting) example example example example 1 2 3 4 constituents kclo.sub.4 23 26 24 14 cuo 17 12 0 0 guanidine nitrate 55 6 2 64 60 guanyl urea 5 0 0 0 dinitramide basic copper nitrate 0 0 1 2 26

performances 1.88 1.80 1.74 1.82 theoretical density pressure exponent 0.21 0.16 0.27 0.31 *vc at 20 mpa (mm/s) 28.3 29.2 33.6 32 **ob (%) -3 -3 -2.9 -3.2 t combustion at 20 2250 2260 2258 2126 mpa (k) gas yield at 1000 k 29.2

30.5 32.5 31.6 (mole/kg) solid residue rate (%) 25.9 23.5 19.2 21.2 *vc = combustion speed **ob = oxygen balance

[0084]the composition of example 4, which offers the best compromise between combustion speed, gas yield and combustion temperature, was treated, for example 5, by carrying out a roller compacting method (pressure between the

rollers of 4.10.sup.8 pa) and dry granulation (forcing of the compacted material by a rotor t hrough a grater equivalent to a screen having a mesh of around 1 mm), upstream of pelleting. The resulting granules, on completion of t he

roller compacting and granulation step, had median granulometry of around 500 .mu.m. They were pelletized (easily, to the extent where t here is no longer a flow problem) in the same conditions as the powders of examples 1 to 4

(pressure of 5.10.sup.8 pa).

[0085]table ii hereinbelow shows the contribution of the roller compacting method on the ballistic performances of the composition.

Table-us-00002 table ii example 4 example 5 constituents kclo.sub.4 14 14 guanidine nitrate 60 60 basic copper nitrate 26 26 method direct pelleting pelleting of granules of the mixture of (without fines) powders originating from dry

compacting performances 0.31 0.38 pressure exponent vc at 20 mpa (mm/s) 32 38.2

[0086]applying the roller compacting and dry granulation method to t he composition according to example 4 causes a rise in combustion speed to 20 mpa of the order of 20%. This increased speed is attributed to improved closeness

of the ingredients after passing through the compacter. The roller compacting phase causes compression and shearing stresses on the mixture, improving the quality of the mixture. Assays conducted at various pressures on the

compacter have confirmed this point. To a certain extent, the ballistics of the formulation is therefore adjustable by the pressure applied to t he rollers during the compacting phase.

[0087]also, the roller compacting and granulation phase generates fines (of low granulometry), which can be reintroduced in the system. This reintroduction also generates greater increase in combustion speed, which may reach 40

mm/s to 20 mpa, in the case of the composition of example 5 with 20% of recycling fines. [0088]pyrotechnic compositions, having the formulation specified in table iii hereinbelow, were prepared by extrusion using 4% by mass of

sodium carboxymethyl cellulose as a binder. The same continuous mixing and extrusion method is carried out .

[0089]according to example 6, the powders are directly introduced (with the binder) to t he device.


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[0090]according to example 7, said powders were pre-compacted and granulated under the conditions specified hereinabove for example 5 and the resulting granules are introduced (with the binder) to the device.

[0091]the performances of the two compositions, prepared in the form of monolithic blocks, are also specified in table iii hereinbelow.

Table-us-00003 table iii example 6 example 7 constituents kclo.sub.4 15 15 guanidine nitrate 49.3 49.3 basic copper nitrate 29 29 dry cellulose gel 4 4 alumina 2.7 2.7 method alimentation with alimentation with powders granules

performances theoretical 1.88 1 .88 density pressure exponent 0.44 0.42 vc at 20 mpa (mm/s) 24.2 28.8 ob (%) -3.2 -3.2 t combustion at 20 mpa (k) 2078 2078 gas yield at 1000 k (mole/kg) 28.8 28.8 rate of solid residues (%) 27 27

[0092]the intervention of the binder is definitely harmful to performance, in terms of combustion speed, of the composition (of example 7 relative to that similar to example 5). All the same, also in this context of extruded product (as

for the pellet product), carrying roller compacting on dry powders results in significantly improving said combustion speed. The gain obtained is of the same order of magnitude, specifically around 20%.

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Pyrotechnics, explosives, & fireworks

V1.0.2 / 01 jul 02 / greg goebel / public domain

* explosives, pyrotechnics, and fireworks -- chemical materials and devices to create fire, smoke, light, heat, noise, or explosions -- have been an important technology for centuries, and continue to be improved. This document

provides a short survey.

[1] definitions

[2] basic principles

[3] black powder / low explosives

[4] commercial high explosives

[5] military high explosives


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[6] detonators & propellants

[7] incendiaries & other pyrotechnics

[8] fireworks

[9] footnote: explosives tagging

[10] comments, sources, & revision history

[1] definitions

* the term "pyrotechnics" means "science of fire", and in principle covers all chemical devices and materials whose purpose is to burn and produce an explosion, fire, li ght, heat, noise, or gas emission. Followi ng this definition,

"explosives" are pyrotechnic materials that cause an explosion, and "fireworks" are pyrotechnic devices used for entertainment.

However, the actual usage of these words is a litt le more confusing and inconsistent. The best way to define them is by description:

y "pyrotechnics" generally refers to chemical materials to create fire, light, heat, noise, or gas emission, but not explosions.Pyrotechnic devices include matches; flares; smoke grenades; airbag inflators; mili tary incendiaries; solid rockets; fuel p ellets for field stoves and other heating units; and quick-release devices used for emergency

exit systems in aircraft, or for staging and shroud ejection systems in space launch vehicles.

y "explosives" always means chemical materials to create an explosion, and they are not generally referred to as pyrotechnics.Explosive materials are used as "bursting charges" for bombs, missile warheads, grenades, and mines; and as "propellants" to fire bullets and artillery shells. They are used as "blasting charges" in militar y or

commercial demolition, for earth-moving for engineering projects, and demolition of buildings and other structures.

Explosives are categorized as "low" or "high" explosives. In low or "deflagrating" explosives, such as black powder, the explosion propagates through the m aterial at subsonic speed through an accelerated burning or

"combustion" process. In high explosives, such as tnt, the explosion propagates by a supersonic "detonation", driven by the breakdown of the molecular structure of the material.

An explosive can be characterized by the amount of energy it releases when detonated, as well as by its shearing and shock effect, or "brisage".

Most modern high explosives are "stable" or "insensitive", meaning they are difficult t o set off by accident. A high-explosive charge generally needs an easily-activated "detonator" or "blasting cap" to cause it to

explode, and sometimes may also need a secondary "booster charge" of i ntermediate sensitivity that is triggered by the detonator to initiate the full explosion. Propellants equivalently need a "primer" and sometimes

a secondary "ignition charge" to set them off.

y "fireworks" can be categorized as a specialized class of pyrotechnic and explosive devices to create visual and sound effects for their entertainment value. Fireworks include firecrackers, skyrockets, smoke pots,whistlers, shells, and roman candles.

back_to_top

[2] basic principles

* most pyrotechnics and low explosives operate by combustion processes, in which a fuel combines with oxygen to release heat, light, smoke, or gas. In such materials, a "fuel" component that burns is mixed wit h an "oxidizing"

component that releases oxygen when heated, since combustion rates would be limited if th e fuel had to rely on atmospheric oxygen for combustion. For example, the fuel in black powder is charcoal and sulfur, while the oxidizer is

potassium nitrate (kno3).

The packaging of a pyrotechnic mixture affects its behavior. Confinement greatly speeds up the combustion process by concentrating heat and hot gas in the reaction. In fact, black powder will simply burn rather than explode unless

packed into an appropriate casing, such as the thick paper shell of a f irecracker.

Burning rate is also increased by the homogeneity of the mixture. Fi ne powders burn faster than coarse grains. Liquid explosives are unsafe because they are extremely homogenous; their mixing is at the molecular level, and so t hey

can be set off by a mild physical shock. Liquid explosives also tend to settle and separate in storage, which changes their chemical properties, and not generally for the better.


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Adding abrasives to an explosive material makes it more sensitive, while adding lubricants like wax makes it more stable. Materials that reduce explosive sensitivity are known as "stabilizers" or "moderators".

* most high explosives operate by a chemical breakdown in their molecular structure, rather than a combustion process between fuel and oxidizer. For example, nitroglycerine has the molecular fo rmula c3n3h5o9. Any small

disturbance, such as heat or physical shock, causes it to decompose into carbon dioxide (co2), water (h2o), nitrogen (n2), and a l ittle excess oxygen (o2).

This process still involves oxidation reactions, but the oxygen is part of the molecule. In the breakdown of nitroglycerine, nitrogen-oxygen atomic bonds are replaced by far more stable carbon-oxygen, hydrogen-oxygen, and nitro gen-

nitrogen bonds, with the process accompanied by a violent release of energy.

* many pyrotechnics, such as flares and fireworks, are designed to emit li ght. Pyrotechnic materials emit light by two processes: incandescence and line emission.

Incandescence, or "blackbody radiation", occurs when solid or liquid particles are heated, causing them to emit a broad spectrum of r adiation. The higher the temperature, the higher the peak frequency of the emission. As a particle

grows hotter, it will glow red, orange, yellow, white, and finally blue. The tot al energy output of an incandescent particle is also proportional to t he fourth power of the temperature, which means that making the combustion twice as

hot makes it sixteen times as bright.

Line emission, in contrast, occurs in a hot gas, a nd produces light through changes in internal electron levels, with light emitt ed only at specific frequencies characteristic of t he type of atom o r molecule making up the gas. If the li ght

frequencies occur in the visible range, they will correspond to fairl y pure colors.

* pyrotechnic materials can be ignited by flame, friction, impact, electrical shock, high ambient temperatures, or even a laser beam. In general, high explosives are designed to be insensitive. They can't be set o ff by a flame or spark,

and have to be set off by a shock from a detonator.

* certain "pyrotechnic" metals, such as magnesium and aluminum, ignite at very high temperatures and burn very hot, releasing large amounts of energy. For this reason, aluminum powder is sometimes added to explosives to enhance

blast effect.

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[3] black powder / low explosives

* while people have devised fiery and smoke-making materials for most of recorded history, the first pyrotechnic material wort hy of the name was black powder, developed by the chinese more than 1,000 years ago. The chinese used

it to make firecrackers and rockets for public entertainment and to frighten enemies in combat.

Black powder migrated to the west in the mi ddle ages. The english monk roger bacon described a formula for it in 1242, writing in code because of the deadly nature of the material. In the 14 th century, black powder led to the

development of new weapons, though several more centuries would pass before it was used i n mining and quarrying, when the technology was finally developed to bore holes in hard rock to place explosives.

In weapons, black powder was used as a bursting agent and a propellant. Black powder charges were used as "petards", or mines, to break down the walls of for tifications, and later as filler i n explosive shells and hand grenades. As a

propellant explosive, black powder was used to fire balls from muskets, as well as stones from primitive cannon called "bombards", which eventually evolved into muzzle-loading artillery. Black powder became god of war, and

remained so until the last decades of the 19t h century.

* early mixtures of black powder consisted of equal weights of charcoal, sulfur, and saltpeter. Saltpeter is a shiny white crystalline material that is found on the walls of caves or in well-aged manure piles; today it is known as

potassium nitrate (kno3). Eventually, the formula for black powder was refined to a mix of charcoal, sulfur, and saltpeter in the proportions 15:10:75 by weight.

Black powder is an excellent explosive in many respects. Its raw materials are cheap, abundant, nontoxic, and environmentally safe. It is stable a nd can be stored indefinitely if kept dr y. It can be easily i gnited with a spark or fuze,

though this is by no means entirely a virtue.

Black powder also has a number of limitations:

y As noted, it has to be kept dry as it absorbs water, and so can be troublesome to handle on naval vessels, or in mil itary operations in damp climates.y It has limited explosive yield. Large quantities of it have to be used to obtain any serious effect, and i ts low brisage meant it left much to be desired for u se in mining, quarrying, and earth-moving.y Its explosive properties are somewhat unpredictable. Sometimes black powder lights off quickly and sometimes not, i ncreasing the hazards of its use.y It burns dirty, creating a l ot of smoke, and fouli ng weapons after a few f irings. Battlefields in the days of black powder were covered with clouds of dirty smoke. Although the first repeater firearms used black

powder as a propellant, the cumulative fouling of t he barrel limited their effectiveness.


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Better explosives were needed and were developed, beginning in the middle of the 19th century. However, the low cost and good properties of black powder make it still the material of choice for fireworks, as will be discussed later.

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[4] commercial high explosives

* in 1846, an an itali an chemist named ascanio sobrero added glycerol to a mixture of nitric and sul furic acids, setting off an explosion that nearly killed him. He had discovered the first high explosive. Sobrero to no surprise decided

that the liquid he called "nitro glycerine" was dangerous. He tried to keep it a secret.

He failed. A swedish chemical manufacturer named alfred nobel began to produce nitroglycerine for rock blasting in 1863. Nitro glycerine can't be detonated by a simple cord fu ze, and so in 1865 nobel devised the first detonator, a

blasting cap consisting of a small black power charge with a cord fuze, to set it off. Nobel's detonator was a significant step forward in the development of modern explosives technology.

It is a liquid explosive and dangerously sensitive. In fact, it was so unsafe that it i s astounding that anybody wanted to be anywhere near it, and nobel's brother emile was killed while working with it. It was often carelessly shipped as

normal freight, without markings to indicate special handling, and terri ble accidents occurred. Nitroglycerine was banned in several nations.

Late in the 1860s, workers found that nitro glycerine that had been frozen was almost impossible to detonate, and so manufacturers began to freeze it for shipment. However, this was clearly a stopgap solution.

Alfred nobel was already working on ways to make a safer explosive. He determined that nitroglycerine was much less sensitive if it was absorbed in " diatomaceous earth", a porous clay that consisted of the deposits of the skeletons

of tiny sea creatures laid down aeons before. This material could be packed into cardboard tubes and reliably transported, handled, and detonated. It could not be set off by a spark or a flame. It was not only safer than nitrogl ycerine, it

was even safer than black powder.

Nobel named it "dynamite", and it quickly became the industrial explosive of choice. Dynamite offered much of the power of nitroglycerine with greatly improved safety. However, it was not perfect. The nitroglycerine in dynamite

tends to "sweat out" in storage, and even form puddles in crates. Cold weather also tends to cr ystallize the nitroglycerine inside a stick of dynamite, making it more sensitive.

Another problem is that nitroglycerine causes dilation of blood vessels. As it can be absorbed through the skin, people who handle dynamite often have pounding headaches. Incidentally, because of this property, nitroglycerine is also

used in small doses as a medicine for people with heart conditions.

The tendency of dynamite to become sensitive in storage made it dangerous to stockpile, and so military fo rces were not enthusiastic about it. Nobel managed to produce another nitroglycerine derivative named "blasting gelatin" that

was more stable than d ynamite, and could also be detonated underwater.

* despite its l imitations, dynamite remained the predominant commercial explosive until the 1950s, when "ammonium nitrate" explosives were began t o become popular.

Ammonium nitrate (an, with the chemical formula nh4no3) is useful as an explosive when mixed with other combustible or explosive substances. In particular, a mixture of ammonium nitrate and diesel fuel known as "ammonium

nitrate fuel oil (anfo)" is commonly used as an industrial explosive. It is also well-known to makers of home-brewed explosives.

The fuel oil i n anfo provides a source of energy, while the ammonium nitrate provides oxygen for the fuel's combustion. However, the breakdown of ammonium nitrate itself produces energy, giving anfo a hefty explosive kick. Anfo

is much cheaper and less sensitive than dynamite, and does not give users headaches, at least not by simply laying hands on it .

In principle, home-brewed anfo is synthesized by mixing diesel fuel and ammonium nitrate fertilizer together until the mix has he consistency of toothpaste. In practice, it's not that simple. Commercial fertilizer doesn't have the

explosive potential of bomb-quality ammonium nitrate, for which access is carefully controlled, and a simple mix of fertilizer and diesel just burns and melts, r ather than explodes.

To actually make an explosive out of f ertilizer, aluminum, zinc, or potassium sulfate (k2so4) have to be added to the mix as boosters. The amount of additive is critical. If too li ttle is added, the mix won't explode, and if too much is

added, it's liable to go off unpredictably. Synthesizing anfo is not a job for the inept.

The potential danger of toying with ammonium nitrate was thoroughly demonstrated on 16 april 19 47. A french freighter loaded with ammonium nitrate fertilizer was docked at texas city, texas, on the gulf coast. The ship caught on

fire in the morning and attracted a crowd of spectators along the shoreline, who believed they were a safe distance away.


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In mid-morning the ship exploded, killing hundreds with the tremendous blast, sending a tidal wave surging over the shoreline, and setting refineries on the waterfront on fire. A second ship loaded with fertili zer exploded after

midnight, but emergency workers were given warning, they evacuated the vicinity of the vessel, and only two people were killed.

Fires burned for six days after the disaster. Official casualty estimates came to a total of 567, but many victims were burned to ashes or literally blown to bits, a nd the official total is believed to be an underestimate.

* ammonium nitrate is also used as the basis for what are called "gelled slurry explosives (gsx)", which are generally used in mining applications. A t ypical formulation would ammonium nitrate and powdered aluminum mixed in

water, with polystyrene powder added as a gelling agent. They form a mudlike mi xture that can be pumped out holes drilled in hard rock, and have high brisage for shattering such rocks.

* coal miners work in an environment full of flammable coal dust, making the use of any kind of true explosive dangerous. As a substitute, they use a "blasting charge" that consists of a cylinder full of liquified carbon dioxide and

containing a heating element. The carbon dioxide expands rapidly when the heating element is activated, and bursts the container, producing a blast but no flames.

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[5] military high explosives

* as mentioned in the previous section, explosives like nitroglycerine, dynamite, and anfo are not very well suited to combat use, though they all have been used in warfare to an extent. Different explosives have been developed for the

battlefield and are widely used by military forces. Of course, military explosives are also used to an extent in commercial applications, but they are relatively expensive, and anfo remains the bulk explosive of choice for civilian uses.

The ideal military explosive is powerful; easy to handle; can be stockpiled for long periods of time in any climate; and hard to detonate except under precisely specified conditions. It also has to be loaded into shells, bombs, and and

the like, and so has to be meltable, so it can be poured into shells; or plastic, allowing it to be "extruded" into shells like caulk from a tube; or insensitive enough to allow it to be packed safely into the shell in bulk form.

* military explosives have been improved for over a century and are now t horoughly refined. The first military high explosive to be put into service was "picric acid", a yellow crystalline substance with the chemical formula

c6h3o7n3, which was first demonstrated by the french in 1885. However, picric acid has a high meltin g point, making the process of fill ing shells with it difficult; re acts with heavy metals to form toxic compounds; and tends to be

sensitive.

The first modern military explosive was "trinitrotoluene (tnt)". Tnt was first discovered in the 1860s, but was not put into service until the german military adopted it in 1902. It was widely used in world war i. It i s relatively

insensitive, and can be melted at low temperature to allow it to be poured into bombs and shells.

The british also used tnt during world war i , but after the war adopted a more powerful explosive named "research department explosive (rdx)". Rdx, more precisely known as "cyclotrimethylenetrinitramine" and sometimes called

"cyclonite", was originally formulated in 1899. It has the in sensitivity of tnt but greater explosive yield.

Tnt and rdx are still the most important military explosives. Other military explosives include:

y "explosive d", or "ammonium picrate". Ammonium picrate has slightly less explosive yield than tnt, but is the least sensitive military explosive. It i s often used in high-velocity armor-piercing shells, since it canstand the intense shock of firing without detonating immediately.

y "pentaerythritol t etranitrate (petn)". Petn is a relatively sensitive explosive, and is oft en used as a booster, or in "detonating cord (detcord)", a type of explosive line used as a detonator and for specialized demolitiontasks.

y "trinitrophenylmethlnitramine" or "tetr yl" is substantially more powerful than tnt, but less stable. It was used as a booster, but now is largely out o f service.* in practice, most mili tary explosives are mixtures of these explosives and other materials. For example:

y Rdx is often mixed with wax or other "plasticizers" to make "plastic explosives", or more fo rmally "plastic-bonded explosives (pbx)". Rdx-based plastic explosives include "composition a", "composition c", and theczech-made "sempex".

Composition a is produced in several different formulations with t he designations "a-1" through "a-5", though a-4 and a-5 are not widely used.


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Similarly, composition c has the formulations "c-1" through "c-4". C-4 is favored by the us army fo r demolition charges, and filler in grenades and land mines.

y Although anfo is not generally suitable to milit ary use, mixtures of an and tnt known as " amatols" were used in both wwi and wwii as a means of stretching the supply of explosives. The proportion of an in the mixranged from 50% to 80%. A mix of anfo, tnt, and powdered aluminum enhancer named "minol" is stil l in use.

y Rdx and tnt are mixed to produce "composition b" and "cyclotol". Rdx, tnt, and aluminum powder are combined in "high brissance explosives" such as "hbx-1", "hbx-3", and "h-6". These formulations are morepowerful than tnt. Hbx-3 has a high proportio n of aluminum powder enhancer for shock effect, and is used in underwater munitions such as depth charges. It appears that hbx-3 is also known as "torpex", though this

may be a slightly different formulation.

y Other explosive mixtures include "pentolite", which is half petn and half t nt; and "tetrytol", which is a mix of tetr yl and tnt.New explosive materials are always being developed. One modern military explosive, "high melting point e xplosive (hmx)" or "octogen", is said to be about 75% more powerful than tnt, and i s now in widespread use as a filler.

One particularly interesting new explosive is "octaninitrocubane". This experimental material is derived from "cubane", a hydrocarbon built around a cubical arrangement of carbon atoms that was synthesized in the 1960s. The

cubical core of cubane makes it very dense, almost twice as dense as gasoline.

In the early 1980s, us army researchers realized if cubane could be modified into a high explosive, its high density would permit faster propagation of breakdown reaction, leading to a more powerful explosive, as well as a more

compact one. Octaninitrocubane consists of a cubic core of eight carbon atoms, with an no2 group attached to each corner of the cube.

Although the new explosive has not been through full evaluation yet, researchers believe that it may be twice as powerful as tnt and very stable, and that i ts breakdown products will be non-toxic carbon and nitrogen compounds. It

appears to be somewhat difficult to synthesize, however.

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[6] detonators & propellants

* detonators have traditionally been made from "fulminate of mercury" or "lead azi de". These are salts of "hydrazoic acid (hn3)", which is a dangerous and unstable liquid explosive, and have the respective formulas of hg(n3)2, and

pb(n3)2.

Fulminate of mercury is highly unstable, and mercury is a r elatively expensive material, not to mention a toxic heavy metal. Fo r these reasons, fulminate of mercury is no longer widely used as a detonator. Lead azide has less yield but

is more stable, and remains the material of choice for detonators.

* black powder had been the only propellant available for firearms and artil lery until the middle of the 19th century, when various chemists began to investigate treatments of paper, wood pulp, and particularly cotton wit h nitric acid

(hno3). These experiments resulted in "guncotton", which had promise as a propellant as it burned quickly and produced a large amount of gas. However, early formulations of guncotton were unsafe to produce and handle. It also

burned too fast, and could cause firearms to blow up in the shooter's face.

Chemists finally managed to create stable formulations of guncotton through processing refinements with sulfur ic acid (h2so4), ether ((c2h5)2o), and alcohol (ch3oh or ch3ch2oh). The first form of smokeless powder to gain

widespread acceptance was "poudre b" or "b powder", synthesized in 1884 by a french chemist named paul vielle.

All such "smokeless" powders were based on nitrocellulose. Cellulose is a long-chain biopolymer found in plants, and treatment with nitric acid r eplaced hydroxyl groups (oh) on the chain with nitrate groups (no3). The higher the

percentage of hydroxyl groups replaced, the more powerful and sensitive the powder became. Creating a reliable smokeless powder required manipulating the percentage of nitrate groups through processing, and adding t he

appropriate moderators and other useful elements.


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In the meantime, in 1875 alfred nobel created a smokeless powder named "ballistite", based on a combination of nitroglycerine and guncotton. This led to another smokeless powder, based on a mixture of guncotton, gelatinized

nitroglycerine, and petroleum jelly, developed by frederick abel and james dewar in 1889. The material was drawn out in a cord and so was named "cordite". Cordite was adopted by the british, who did not trust b powder, and by

world war i cordite was the dominant propellant.

* modern propellants are categorized as "single-base", "double-base", and "mult i-base" or "composite" powders:

y Single-base powders such as cordite are mostl y nitrocellulose. They burn cool and cause little barrel wear.y Double-base powders are mixtures of nitro glycerine and nitrocellulose such as ballistite, and burn hotter.y Composite powders are modern formulations that do not contain nitrocellulose or nitroglycerine, instead using more modern propellants that burn cool but are as powerful as double-base powder.

Firearms now generally use single-base or composite powders. Double-base powders are now generally used as a propellant for solid-fuel rockets.

Smokeless powders are not tru ly smokeless, but they burn much more cleanly than black powder. Burning rate of smokeless powders, as with other explosives, can be controlled by varying the size of the powder grains. Large grains

burn relatively slowly, and so are appropriate for use i n pistols and other weapons with short barrels. Grains can also be perforated so they burn from the inside as well as out.

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[7] incendiaries & other pyrotechnics

* the military also makes heavy use of incendiary materials. Incendiary weapons have long been used in combat, for example, the "flaming arrows" used by apaches to set wagons on fire in western movies. In the 7th century ad,

byzantine greek alchemists found that a mix of pitch, naphtha, sulfur, and petroleum wou ld burst violently when ignited, and named the mixture "greek fire". The empire's milit ary used it to defend constantinople from invading

saracens. Later, in naval fighting during the age of sail, cannonballs were oft en heated red-hot before firing in hopes of sett ing an enemy vessel on ablaze.

Modern military incendiary munitions consist of "napalm", "fuel-air explosives (faes)", and metallic compositions. Napalm is simply gasoline to which a t hickener has been added to make the burning fluid viscous and sticky. The

original world war ii form of napalm used a soapy thickener named "sodium palmitrate", leading to the name "na-palm". Modern "napalm b" uses polystyrene plastic beads as a thickener.

Faes spray out an aerosol cloud of a hydrocarbon liquid such as ethylene, and then ignite it to create a flaming e xplosion over a wide area.

Aluminum has already been mentioned as an incendiary metal. Other incendiary metals include zirconium, magnesium, titanium, and depleted uranium. They all burn at very high temperatures. A particularly useful metallic

incendiary is "thermite", which is a mix of ferrous oxide (fe2o3, essentially rust) and aluminum. The thermite reaction is as shown below:

fe2o3 + 2al -> al2o3 + 2fe

The reaction burns very hot and releases a tremendous amount of energy. Thermite is is o ften used in demolition grenades to burn or melt down military gear that has to be abandoned to an enemy.

One new scheme uses a "combustible foil" based on pyrotechnic metals to perform emergency welds. The foil contains thin alternating layers of metals such as nickel and aluminum. The foil is ignited by a match or a 9-volt battery,

and instantly ignites over its entire surface. It wor ks in a vacuum or underwater, and can be used by soldiers for emergency field repairs. The combustible foil could also be used for detonators and heating devices.

* white phosphorus was also once used as a military incendiary. Elemental phosphorus comes in two forms, a "red" amorphous form, and a "white" form arranged as tetrahedral units of four atoms. Red phosphorus is relatively easy to

handle, but white phosphorus ignites spontaneously at room temperature. White phosphorus is now mainly used to generate smoke.

White phosphorus also serves a role in the most common pyrotechnic device, the safety match. The match was invented by an english chemist named john walker in 1826, when he was mixing chemicals with a small sti ck and

accidentally scraped the stick on a r ough surface. It caught fire. Walker fo llowed up the lucky accident by developing and selling the first matches.

The basic design of the match remains much the same as walker' original invention. The head still consists of an oxidizer such as potassium chlorate (kclo3); a fuel such as sulf ur or r osin; and a binder (glue). Modern safety matches,

however, have a tip of phosphorus trisulfide (p4s3). The stem is dipped in a fireproofing agent to keep it from burning too easily, and the head is coated with paraffin to k eep it dry.

The striking surface on the package of matches is coated with powdered glass and red phosphorus mixed in a binder. When a match is scratched over the striking surface, the red phosphorus in the surface i s converted to white

phosphorus by heat of f riction, and the phosphorus trisulfide burns in the air. This ignites the fuel and oxidizer, which creates a sustained flame. The match will not easily ignite if scratched on any ot her abrasive surface.

* other pyrotechnic materials are used as heating fuels, in fuzes or flares, to create smoke, fill up automotive airbags, or propel rockets. Some common pyrotechnic devices include:


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y Heating fuel pellets. Calcium-based fuels mixed with iron oxide can generate moderate heat without producing gas. During world war ii , small pyrotechnic devices made of this mixture and a fu ze were built into cansof rations so t hat they could be warmed without a stove, and such fuel pellets can still be bought for small camp stoves.

y Fuzes. Pyrotechnic fuzes are oft en made of sulfur, silicon, t ungsten, and boron. They can be pressed into colu mns that burn for a specific interval and then initi ate a larger reaction. Such fuzes are used to control thetiming sequence in various aerospace devices, including the explosive bolts that release emergency-exit hatches and spent rocket stages, and are used for time delay in hand grenades.

y Flares. There several classes of flares for military and commercial use. Commercial red roadside warning flares are made with strontium compounds and an oxidizer. Military night-illumination fl ares are made withparticles of magnesium, mixed with an oxidizer and binder.Military aircraft often carry thermal f lares to distract heat-seeking missiles. At first, ordinary signal fl ares were used in this r ole, but missiles became more sophisticated, and so flares became more sophisticated as

well.

Modern decoy flares consist of teflon plastic mixed with a fluorine compounds as an "oxidizer". They may contain two "stages" that burn at different t emperatures at different times. The latest "pyrophoric" flares are

made from ribbons of metal that oxidize at a rapid rate just short of burning in order to simulate the moderate temperatures of a jet exhaust. Missiles have become so smart that aircraft are now moving towards laser

systems to confuse them, as flares are no lo nger up to the job.

y Flash powder. Aluminum or magnesium powder mixed with an oxidizer results in a "flash powder" that can be used to generate a bright flash of light and a loud bang. Flash powder can be used as a light source fornight photography.

y Smoke grenades. Militar y smoke grenades are made either with phosphorus, or with sugar as a fuel mixed wit h an oxidizer such as potassium chlorate, along with organic dyes to generate colored smoke. Sugar burnsat a low t emperature and will not degrade the dyes. Tanks and other armored vehicles often mount smoke-grenade launchers to allow them to lay down a smokescreen for concealment, and smoke grenades and rocket

warheads are often used for target marking and helicopter l anding zone designation.

y Airbag inflators. Automotive safety airbags have to be inflated almost instantly, which requires a pyrotechnic that generates a large amount of gas quickly, but does not cause fire or any more blast than necessary.This requirement led to the development in the 1970s of small, cheap, solid-propellant inflators, based on t he combustion of "sodium azide (nan3)" with an oxidizer, rapidly producing a great quantity of nitro gen gas

that can inflate an airbag in a little over 50 milliseconds. Sodium azide consists of interlinked lattices of ions of sodium and azide, a group of three chemically bound nitrogen atoms. A shock disrupts the lattice

structure, and the sodium combines with oxygen, while the nitrogen atoms regroup into pairs to form a large quantity of nitrogen gas.

y Solid fuel rockets. Most of the small rockets used in world war ii used double-base powder as a propellant, but during the war the us jet propulsion laboratory (jpl) developed a slower burning solid fuel based onasphault, mixed with ammonium perchlorate (nh4-clo4) or potassium perchlorate oxidizer (kclo4) and aluminum powder. The only problem was that the asphault tended to flow, particularly in hot environments, and

the rockets had to be stored nose-down.

After the war, this scheme evolved to modern solid rocket fuels based on certain forms of s ynthetic rubber, mixed with a mmonium perchlorate oxidizer and a high concentration of aluminum powder. The synthetic

rubber not only provided a fuel source, but also acted as a "binder" that could be cast in a huge solid block, without voids or cracks that would cause uneven combustion, that could be safely stored for a long period

of time without degradation. Each solid-fuel booster on the space shuttle weighs 500 tonnes.

One interesting application of modern solid-rocket fuel is for mine disposal. Flares filled with solid-rocket fuel have been designed so they can be set up over a mine on li ttle pop-out legs. The hot exhaust burns

through the mine casing and sets the explosive filling on fir e.

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[8] fireworks

* while fireworks may not seem like high technology, they are a highly refined art. There are two basic schools for fireworks fabrication, the oriental and the italian. In the us, fir eworks are manufactured by a few concerns, most of

which run in italian families, such as th e zambellis and the gruccis.

Nearly all pyrotechnic materials except for high explosives are used in fireworks. The basic constituent of many fireworks is, as mentioned earlier, black powder, but flash powders and smoke-generating pyrotechnics are used as well.

Simple firecrackers and rockets are made from black powder in paper cases. Sparklers are made from a t hick slurry consisting of fuels, binders, and oxidizers into which wires are dipped. Whistling fireworks use gas-generating

pyrotechnics that are packed into narrow tubes that create the whistle when the gas escapes.


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Roman candles consist of a set of bright "stars" that generate light and color, packed into a paper tube in layers of black powder. As the black powder burns down from t he top of the tube, it ignites each layer of black powder in turn,

spitting out a star.

The stars are made of mixes of pyrotechnic metals, salts, and bi nders such as resin and gum. Stars in oriental fi reworks are rolled into shape, while italian stars are generally made from cakes and cut into cubes. The round oriental stars

can have multiple layers, causing their appearance to change as they burn.

Early stars and other illuminating elements could only obtain white and gold effects, using saltpeter. Modern stars obtain a wide range of color effects using strontium compounds for reds; titanium, magnesium, or aluminum for

whites; copper compounds for blue; barium compounds for greens; incandescent steel and charcoal particles for gold; and sodium compounds for yellows.

Clever chemistry has to be employed to get the desired results. The strontiu m and barium compounds aren't stable in storage, for example, and have to be synthesized through chemical reactions during the pyrotechnic process. Copper

compounds will break down if the pyrotechnic process is too hot, destroying the color, so the firework has to be carefull y designed to burn at a low t emperature.

A "setpiece" is an obscure form of fireworks display that is undergoing something of a revival. It consists of hundreds of t ubes of color-generating fireworks mounted on a wooden frame in a graphics pattern and linked with a fast-

burning black powder fuse taped to the frame. The fuze sets off all the tubes quickly to generate a vi vid display, and can also set off pinwheels and other fireworks attached to t he display.

Large skyrockets are also used in public displays. They use a black powder propellant, sometimes mixed with other pyrotechnic materials so they leave a spectacular trail, and have a payload consisting of stars or other pyrotechnic

elements dispersed by a black powder bursting c harge.

However, the main firework for public spectaculars is the "shell". Shells can be built to produce a variety of effects:

y "chrysanthemums" generate a more or l ess symmetrical burst of fiery streaks.y "salutes" use flash powder to generate a bright flash and lou d bang.y A "palm tree" leaves a trail behind it, and bursts into bright arching "fronds".y "willows" generate drooping trails of light.y A "split comet" generates fireburst that then generate other bursts, which may generate further bursts.

Shells consist of a payload and a "lift charge" of black powder that lifts it into the sky. The shell is stuffed down a pvc pipe mounted in a sandbox, and lit off by an i ncendiary fuze or, more commonly in big fireworks displays, by an

electric spark from a "squib". When the shell i s fired, a time-delay fuze, or "spegette", inside the shell is lit, and burns down to set off a black-powder charge that bursts the shell and disperses the stars.

Oriental shells are spherical, while italian shells are cylindrical. Bursting charges in ori ental shells may consist of rice hulls impregnated with black powder to increase the flash of the burst. Ori ental shells are appropriate for

generating symmetrical displays, such as chrysanthemums.

Italian shells burst in a more i rregular fashion, but they can be designed with multiple fi rework stages or "breaks", connected by spegettes, that detonate consecutively. For example, a three-break italian shell might consecutively

disperse a burst of red, white, and blue stars.

Multiple-break shells can be very elaborate. The blast charge may ignite a set of stars so the shell's launch is suitably spectacular, and the stages may contain such elements as whistling pyrotechnics as well as stars.

Sophisticated fireworks displays often use elaborate control systems to sequence the ignition of fireworks, and synchronize them with sound and laser effects.


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One of the more interesting fields in modern f ireworks are indoor fireworks displays, produced by specialist firms such as lu natech indoor fireworks of california. Such displays are used in rock concerts and other entertainments, and

use conventional fireworks technology, modified with strict safety standards in mind to ensure no toxic emissions and appropriate safety for performers and audience.

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[9] footnote: explosives tagging

* one interesting area of explosive technology are "tagging" systems that allow the identification of t he origin of an explosive that was used, for example, in a terrorist bombing. While analysis of the chemical composition of blast

residues can help identify the type of explosive, the ability to trace explosives by production batch is much more useful.

One explosives tagging technology has been around for several decades. Microtrace incorporated of blaine, minnesota, markets a "microtag" scheme that was invented in the 1970s by a chemist at 3m corporation named richard

livesay.

3m developed and sold the microtag system, which is based on tiny chips, each about t he size of a grain of pepper, that are built as a stack of up to 10 colored layers. A batch of chips with a particular "rainbow" code is mixed with a

particular batch of explosives to permit its identification. A us government-mandated test of the ta gs that required their use in 1 % of commercially produced explosives made from 1977 through 1979 demonstrated no real problems

with the technology, and even led to the solu tion of one bombing. The swiss, who were early adopters of t he technology, have solved hundreds of bombing incidents through the use of the tags.

However, a disastrous accident at an explosives factory in 1979 was blamed on the tags, and led to a lawsuit against 3m. Though the company won the case, they got out of the taggant business, selling it to li vesay, who fou nded

microtrace. Most of microtrace's customers use the microtags to protect goods, like shampoo and alcohol, from counterfeiters.

A subtler tagging technology is being marketed by isotag llc in houston. The isotag scheme is based on inert heavy molecules, uniquely keyed by selectively substituting deuterium (heavy hydrogen) atoms for ordinary hydrogen in the

molecular structure. It has been used in applications such as identifying batches of petroleum sent through pipelines, and for tagging batches of ammonium nitrate.

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[10] comments, sources, & revision history

* i am by no means an explosive enthusiast. This document evolved out of a longer writeup named dumb bombs and smart munitions. An early version of dumb bombs included a short survey of explosives, but i t didn't seem to fit

very well, so i removed it and merged it other interesting information i found on pyrotechnics and fireworks to create this document.

Of course a warning is required for a document on explosives. There's not much in t he way of practical specifics in this document, so it's unlikely that anyone could use it t o cause much trouble, but i would still suggest that taking

advice on synthesizing explosives from somebody who's never done it and immediately admits he's no expert might be unwise.

* writing this document brought back memories of my milit ary tour of duty in the early 1970s. No o ne who was ever a soldier can forget watching a parachute flare floating down through the night, scattering its harsh white light over

the landscape. When i was stationed at fort hood in texas, i also occasionally saw flashes of light that li t up the sky, a pparently due to photoflash flares dropped by reconnaissance aircraft over the range area.

The idea of the self-heating ration cans made during world war ii was interesting. Although i have seen cheesy little camp stoves that used fuel pellets, i never saw a self-heating can, and why such a seemingly good idea was

abandoned is an i nteresting question. In a pinch, a soldier could more o r less heat up a can of c-rations by punching a hole in the box, sti cking the can in the hole, and burning the box. It was usually better to sit the can on the muffl er

pipe of a generator, though this could lead to messy consequences if it was forgotten.

Modern mre military rations, so i have heard, include a pyrotechnic cardboard "sandwich" that gets hot when doused with water, and transmits the heat to the meal through a matrix of staples driven through the cardboard.

I was in the signal corps and never played much with weapons beyond my m-16, but heard interesting stories about c-4 and detcord. C-4, i was told, could be burned, but it was sensitive to shock, and stepping on it to put it out was

dangerous. I heard some stories about some of the nasty things that could be done with it, but won't repeat them here for fear of giving people bad ideas.

People who used detcord compare it to "waxy closeline cord" and say it was a remarkably flexible tool. For example, detcord could be used to cut a 55-gallon fuel drum in half, to use in a latrine or whatever, simply by wrapping a

length of detcord around it and detonating it. It is also used in aircraft escape systems, for example to shatter a canopy before firi ng an ejection seat. Shattering the canopy is faster and more reliable than blowing it off, and aircrew will

not collide with the canopy on ejection.

* sources for this document include:


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y "airbags" by robert e. Reish, scientific american, june 1996, 116.y "pyrotechnics" by john a. Conkling, scientific american, july 1990, 96:102.y "an end to anonymous bombs?" by otis port and others, business week, 12 august 1996, 84:85.y "foils join in a flash", machine design, 16 january 1997, 76.y "rocket's red glare" by roy attaway, popular mechanics, july 1997, 54:57.y "working knowledge: aerial fireworks" by george r. Zambelli sr, scientific american, july 1999, 108.y "powerful explosive blasts onto scene" by c. Wu, science news, 22 january 2000.

Other information was obtained from various encyclopedias, and interestingly the microsoft encarta on-line encyclopedia has some nice, well- organized little writeups on explosives and pyrotechnics. I also found some information in

tv shows on explosives and fireworks broadcast on t he history channel and the discovery channel.

I picked up various small items by surfing t he web, but as far as i know this is the only comprehensive document on the subject on the internet. That's a s hame as i would certainly like to get a few more realit y checks from people with

professional experience.

* revision history:

v1.0 / 01 dec 99 / gvg

v1.1 / 01 mar 01 / gvg / cosmetic rewrite, minor additions.

v1.0.2 / 01 jul 02 / gvg / cosmetic rewrite, minor changes.

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home

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media & press

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Glossary of pyrotechnic terms

1.3g explosives formerly known as class b special fireworks. Items classified as 1.3g explosives are display fireworks.

1.4g explosives formerly known as class c common fireworks. Items classified as 1.4g explosives are consumer fireworks intended for use by t he general

public.

Apa standard 87-1 the standard for construction and approval for transportation of f ireworks, novelties, and theatrical pyrotechnics.

Aerial shells a fireworks device designed to be launched into the air fo r use in a fireworks display.

Aerial shell a cartridge containing pyrotechnic composition, a burst charge, and an internal time fuse or module, that is propelled into the air from a mortar.

Assistant a person who works under the supervision of the pyrotechnic operator.

American pyrotechnics association trade association for the fi reworks industry.

Atfplease see bureau of alcohol, tobacco, and firearms

Barge water vessel from which fireworks are discharged.

Barrage a rapidly fired sequence of aerial fireworks.

Battery a collection of fireworks devices, such as a group of mortars (finale battery) or a bundle of roman candles (candle battery,) fused together in such a

manner that they are fired within a short period of time.

Black match a fuse made from string that is impregnated with black powder.

Black powder material found in fireworks. This material can be used as a propellant charge, to produce sound, as a constituent of other compositions, or in

the ignition fuse or timing system of fireworks. Also known as gun powder.

Bouquet fountains fired in groups.

Break an individual burst from an aerial shell, generally producing either a visual effect (stars) or noise (salute).

Bureau of alcohol, tobacco, and firearms (atf) federal agency which regulates the licensing and storage of display fireworks. This agency monitors the

importation, manufacture, distribution, and storage of display f ireworks.

Cake a chain-fused firework that propels a series of aerial shell, comet or mine effects into the air from collectively attached tubes.

Chain fusing a series of two or more aerial shells fused to fire in s equence from a single ignition.

Chemical composition all pyrotechnic and explosive composition contained in a fireworks device. Inert materials (such as clay used for plugs or organic

matter used for density) are not considered to be part of chemical composition.

Comet a pellet of composition which is propelled from a mortar or shell and produces a long tailed effect. Large comets are constructed much like aerial

display shells, with attached lift charge ready for lo ading into mortars.

Consumer fireworks also known as 1.4g fireworks. Fireworks that are intended for u se by the consumer. The permitted usage of consumer fireworks varies

by state. Examples are fountains, cones, and firecrackers.


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Consumer product safety commission (cpsc) federal agency which regulates consumer 1.4g f ireworks.

Department of transportation (dot) federal agency which controls the transport of all hazardous materials including fireworks. This organization also

assigns all legal commercial fireworks with an ex number.

Discharge site the area immediately surrounding the fireworks mortars used for an out door fireworks display.

Display fireworks (formerly known as special fireworks) large fireworks articles designed to produce visible or audible effects for entertainment purposes

by combustion, deflagration, or detonation.

Display site the immediate area where a fireworks display is conducted, including the discharge site, the fallout area, and the required separation distance

from mortars to spectator viewing areas, but not spectator viewing areas or vehicle parking areas.

Dud any device in which the fuse or igniter fails to ignite the m ain pyrotechnic charge. The term, dud, is reported to have originated as an acronym for

dangerous unexploded device.

Electrical firing unit a device that provides and controls the electric current used to ignite fireworks during a display.

Electrical firing unit, automatic a panel or box that o perates automatically to provide the source of electric current used to ignite electric matches.

Electrical firing unit, handheld a small, handheld unit with manually operated switches that control the flo w of electric current t o electric matches attached

to fir eworks devices.

Electrical firing unit, manuala panel or box with manually operated switches that control the flow of electric current to electric matches attached to

fireworks devices.

Electrical ignition a technique used to ignite fireworks using a source of electric current.

Electric match an electric device that contains a small amount o f pyrotechnic material that ignites when current flows through the device.

Ex number the identification number assigned by dot to a commercial fireworks device. All legal commercial fireworks must have an ex number.

Explosive (regulatory definitions)

Atfany chemical compound, mixture, or device with the primary or common purpose being to function by explosion. The term includes, but is not limit ed

to: dynamite, black powder, pellet powder, initiating explosives, detonators, safety fuses, electric matches, detonating cords, igniter cords, and igniters.

Nfpa the term explosives includes any material determined to be within the scope of ti tle 18, united states code, chapter 40, importation, manufacture,

distribution, and storage of explosive materials, and also includes any material classified as explosive by the hazardous material regulations of dot.

Explosive (technical definition) any material that is capable of undergoing a self-contained and self-sustained exothermic chemical reaction at a rate that is

sufficient to produce substantial pressures on their surroundings, thus causing physical damage. Explosives fall into 2 classes, detonating and deflagerating.

Explosive composition any chemical compound or mixture, the primary purpose of which is to function by explosion, producing an audible effect.

Fallout area the designated area in which hazardous debris is i ntended to fall after a pyrotechnic device is fired.

Finale a rapidly fired sequence (barrage) of aerial fireworks, typically fired at the end of a display.


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Low level fireworks (also ground-to-air fireworks) any of a class of fireworks devices that either perform below approximately 200 feet (6 0 m) or begin

their display at ground level and rise to complete t heir effect. Some examples of low level fir eworks are comets, mines, roman candles, and many consumer

fireworks.

Manual ignition a technique used to ignite fireworks using a handheld ignition source such as a fusee or portfire.

Mine a device containing multiple pyrotechnic effects that are simultaneously ignited and dispersed into the air from mort ar or tube.

Monitor the individual at a fi reworks display responsible for observing the perimeter of the firing site and insuring that security personnel or barriers keep

spectators at a safe distance. Usually provided by the organization sponsoring the event.

Mortar a tube from which certain aerial devices are fired into the air.

Mortar racksturdy wooden or metal frames used to support mortars in an upright position usually above ground.

Mortar trough above ground structure filled with sand or similar material into which mortars are positioned.

National fire protection association (nfpa) organization which provides several standards that sssoutline recommendations for t he manufacture, storage,

transportation, and execution of fi reworks.

Nfpa standard 1123code for fireworks display

Nfpa standard 1124code for the manufacture, transportation, and storage of fireworks and pyrotechnic articles

Nfpa standard 1126standard for the use of pyrotechnics before a proximate audience

national council on fireworks safetya non-profit group that promotes the safe enjoyment of consumer fireworks.

Novelty a device containing small amounts of pyrotechnic and/or explosive composition but does not fall under the category of consumer fireworks. Such

devices produce limited visible or audible effects. Examples are snakes, tanks, poppers, and snappers.

Occupational safety and health administration (osha) federal agency that i nspects fireworks manufacturing plants. Osha not only regulates non-fireworks

specific aspects of plant safety (i .e. Housekeeping, electrical requirements, employee training), but also the fireworks-related standards of nfpa standard

1124.

Operator the person with overall responsibility for the operation and safety of a fireworks display. The operator is also responsible for storing, setting up,

and removing pyrotechnic materials or devices after a performance.

Placard warning symbol of a square-on-point configuration mounted on each side and each end of a truck, r ail car, or frei ght container which informs the

public and emergency personnel of the hazardous nature of cargo, as specified in 49 cfr, 172.

Portfire a long tube containing slow-burning pyrotechnic composition that is sometimes used to ignite fireworks at outdoor fireworks displays.

Proximate audience an audience that is closer to pyrotechnic devices than allowed by the nfpa 1123, code for the outdoor display of fireworks.

Pyrotechnic device any device containing pyrotechnic materials and capable of producing a special eff ect.

Pyrotechnic material a chemical mixture used in the entertainment industry to produce visible or audible effects by combustion, deflagration, or detonation.


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Pyrotechnic special effect a special effect created through the use of pyrotechnic materials and devices.

Pyrotechnics controlled exothermic chemical reactions that are timed to create the effects of heat, gas, sound, dispersion of aerosols, emission of visible

electromagnetic radiation, or a combination of these effects to provide the maximum effect from th e least volume.

Quickmatch also known as an instantaneous fuse. Black match that is encased in a loose-fitting paper or plastic sheath to make it burn extremely rapidly.

Quick match is used for aerial shells and for simultaneous ignition of a number of pyrotechnic devices, such as lances in a ground display piece.

Ready box a storage container for aerial devices for use during set-up and display.

Ready box tender assistant who controls and dispenses the contents of rea

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