Green pyrotechnics. Doru Adrian GOGA Military Technical Academy - Bucharest

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1 Green pyrotechnics Doru Adrian GOGA Military Technical Academy - Bucharest 1.1 Introduction Explosive materials such as high explosives, propellants and pyrotechnics are used in weapon systems to perform a variety of functions. They provide the energy required to deliver the payload to the target and to obtain the desired terminal effect. Because of their high energy content, these materials are sensitive and can be initiated by stimuli such as heat, shock, friction, impact, and electrostatic discharge. All of these stimuli may be encountered in development programs, and later in the manufacture, transport, storage, and operational or training use of explosive materials. The careful and judicious selection of explosives is important since it will affect the sensitivity and safety of munitions and the vulnerability of weapon platforms. Trade-off with performance can be made, but in general, the more powerful the explosive used, the more sensitive it is to stimuli, and the more protection must be provided to shield munitions in hazardous areas. Since in many applications space is limited, it is often impossible or unfeasible to provide the increased protection. Therefore, in qualifying explosives, National Authorities must exercise caution and concern for the sensitivity and the suitability for service of the explosive materials being considered for all military applications. Further, munition designers should select the least sensitive explosive material that meets the operational requirements defined for their application. An explosive material is a substance (or a mixture of substances) capable by chemical reaction of producing gas at such temperature and pressure as to cause damage to the surroundings. Included are pyrotechnic substances even though they may not evolve gases as they react. This document refers only to those explosive materials whose application requires that they react reliably on demand. The term "explosive" thus includes all solid and liquid materials variously known as high explosives and propellants, together with igniter, primer, initiatory and pyrotechnic (e.g., illuminant, smoke, delay, decoy, flare, and incendiary) compositions. Pyrotechnic compositions are substances (or a mixture of substances) that when ignited, undergo an energetic chemical reaction at a controlled rate intended to produce on demand and in various combinations, specific time delays or quantities of heat, noise, smoke, light or infrared (IR) radiation. Pyrotechnic compositions may be used to initiate burning reactions such as in igniters. This work will approach a multitude of pyrotechnical subjects. The word Pyrotechnics comes from the Greek words pyro meaning "fire" and tekhnikos "made by art". Often, there is some confusion between pyrotechnics and explosives science or detonics. This can be explained by the explosives classification for their intended roles, as represented in figure 1.

2 EXPLOSIVE MATERIALS An explosive material is a substance (or a mixture of substances) capable by chemical reaction of producing gas at such temperature and pressure as to cause damage to the surroundings Primary explosives A substance or mixture of substances used to initiate a detonation or a burning reaction. In their intended role these materials are sensitive to a range of thermal, mechanical and electrical stimuli Booster explosives An explosive material used to augment and transmit the reaction (initiated by the primary explosive) with sufficient energy to initiate a detonation reaction in the main charge high explosive High explosive A material that is used as a detonating final charge Gun powders and propellants This is a substance (or a mixture of substances) that is required to burn in a controlled manner within a gun combustion chamber producing hot gases capable of propelling a projectile at high velocity. Combustible cases may also be included as they contribute to the overall energy of the propellant Pyrotechnic Compositions These are substances (or a mixture of substances) that when ignited, undergo an energetic chemical reaction at a controlled rate intended to produce on demand and in various combinations, specific time delays or quantities of heat, noise, smoke, light or infrared (IR) radiation. Pyrotechnic compositions may be used to initiate burning reactions such as in igniters Figure 1 Explosive classification

3 Pyrotechnics is the technique, the science and the art to create, to maintain and to manage the FIRE. The study, the design or the development of pyrotechnic compositions impose anywhere and all the time, theoretical and experimental tests. Today, Pyrotechnics is a frontier multidiscipline science regarding: Study of pyrotechnic compositions combustion phenomena; Study of physical, chemical, energetic, sensibility, stability properties of pyrotechnic compositions; Manufacture and preparation methods of pyrotechnic compositions and their loading process into the pyrotechnic systems; Special pyrotechnic effect study (illumination, signaling, smoke Vis and IR screening, colored smoke, tracer) and the interactions with the environment (air, water, earth, people). Pyrotechnic compositions / systems classification A pyrotechnic system is an ensemble of pyrotechnic compositions or pyrotechnic layers, structures, mechanical components, pieces or accessories used to integrate or accomplish specific operational missions. We can considere a pyrotechnic chain similar to multilayer pyrotechnic compositions, and this can be considered a part of a pyrotechnic system. Depending on their intended role, pyrotechnic compositions/systems can be divided as: Illumination flare (cartridges, projectiles, mortar bombs, rocket hand fired, ground illuminating flare etc.), are used for signaling, illumination, able to light by night in order to facilitate the different objectives; Illuminating pyrotechnic systems may be dropped from aircraft, fired from rocket or artillery, or deployed by flare guns or handheld percussive tubes. Flash-bang (grenades, charges) used to emit an intensely loud bang and a blinding flash, sufficient to cause immediate flash blindness, deafness and inner ear disturbances. Exposed personnel experience disorientation, confusion and loss of coordination and balance. Tracers (devices, bullets, projectiles) are used to make visible the projectiles trajectories by day or by night. This enables the shooter to make aiming corrections without observing the impact of the rounds fired and without using the sights of the weapon. Signaling (Handheld cartridges, star clusters, star parachutes, smoke parachutes, surface trip flares, etc.) uses to signal by day or by night at distance; Pyrotechnic signals are used in difficult situations, when normal communication means like radio, telephone are not effective in certain tactical situations. Pyrotechnic signals are prescribed at command level. incendiary (bullets, bombs, projectiles etc.) designed to catch fire, to burn some objectives inflammable or not; Smoke screening (generators, grenades, proiectiles, mortar bombs etc.) The generation of a thick and dense cloud is used to conceal movement of vehicles and troupes, to camouflage, to induce deception, to adopt a defensive or offensive strategy. Infrared decoy flare (flare cartridge, flare dispenser) is an aerial countermeasure used by a plane or helicopter to counter a heat-seaking / infrared homing missile; the radiation emitted by the flare has the goal to make infrared-guided missile seek out the heat signature from the flare rather than the aircraft's engines. Training and simulators (booby trap simulator, ground burst simulator, hand grenade simulator, explosive simulator etc.), are used during training and military

4 exercises. They simulate simulates hand grenades, booby traps, land mines, and rifle or artillery fire; in combat they can realize the diversion and confusion to enemy; Prime ignition sources (matches, stab, percussion and electric primers etc.) used to facilitate the ignition of pyrotechnic devices by friction, impact, temperature, flame or other stimulus; Delay (fuse, delay device) is a pyrotechnic composition filled in some devices used provide a specific time between activation and production of the main effect; Heat generating compositions for thermal batteries used sources to provide ionic conduction in a molten electrolyte and to maintain the working temperature of the battery during the discharge of the electrochemical elements. Base bleed (devices attached to great caliber projectiles), used to generate gases and reduce the drag coefficient and to increase the maximum range; Gas generators (generators), used to generate a large quantities of gas, to power turbo-pumps in rocket motors, to deploy airbags; Other applications. Combustion or deflagration of pyrotechnic composition are complex oxidizing / reduction process, where the oxidation of some components called carburants is produced simultaneously with the reduction of other components called oxidants. The pyrotechnic compositions are mechanical mixtures of two or more components which are solids most of the time. The degree of homogeneity of these compositions, the nature of components and the proportion of components will determine their properties. The combustion process is carried out in so called the reaction space where the heat transfer is done little by little, from reaction products to inactivated composition. In order to get the specific reaction conditions, is required a local increase of temperature which is realized by using some special compositions (first fire). 1.2 General conditions required for the pyrotechnic compositions/systems Combustion compositions and the functioning of the pyrotechnic systems is the base of generating special pyrotechnic effects: illuminations, signaling, smoke, incendiary, catch fire, simulation and training etc. In order to safely store, transport, handle and operate the pyrotechnic systems/ compositions, some requirements must be aquired for pyrotechnic compositions as: Chemical and physical stability; Sensitivity to different stimuli; Performance characteristics; Low toxicity or friendly impact on the environment. The main technical conditions required for the pyrotechnic compositions/systems are: - Maximum pyrotechnic effect per mass unit composition; - The combustion has to uniformly develop at a constant rate, according to all the environmental conditions (pressure and temperature); - A good physical-chemical stability for the whole life time; - Appropriate sensitivity and reduced explosive reaction to the mechanic, thermal and electric agressions; - Non violent explosive properties (explosivness) and the lowest risk of a mishap; - The absence of toxical reaction products for the human body and the environment; - Easy, efficient and economical manufacturing. It s not always easy to design and obtain a composition or pyrotechnic system which would meet all these requirements. More often, other requirements are added to the

5 mandatory ones, some of them of tactical nature, which can t be quantified into a technical language. It s the pyrotechnician s job to implement the specific requirements and to find practical ways to insure that all the required conditions are followed. Despite all the difficulties, including the intuitive ones, we can get the desired results through a better understanding of the raw materials, production processes, testing and assessment methods. There are two different situations, in reference to the requirements analysis of a pyrotechnic composition/system: 1. Knowing the system/composition and is required the verification of its specification; 2. Designing and manufacturing of a new composition/system it s starting from general, tactical and performance requirements. 1.3 General notions about pyrotechnic compositions/systems manufacturing The pyrotechnic compositions are homogenous mixtures of multiple components. It is relatively easy to mix a few solid substances. Nevertheless, to insure the mixture homogeneity or for getting the ideal progress conditions reaction it s mandatory to follow successive steps, when the elements of the pyrotechnicl composition suffers changes or modifications. The degree of homogeneity or the mixture uniformity is affecting the chemical composition of the pyrotechnical mixture, with several implications over the performance characteristics, stability and sensitivity of the pyrotechnic system. Thereby, in order to prepare and charge a pyrotechnic composition the following steps are necessary: 1. Components preparation; 2. Pyrotechnic composition preparation (mixing, granulation, draying); 3. Completing the composition preparation (draying, granulometric sorting out); 4. Pyrotechnic composition charging (by pressing compressing or other methods). The manufacture and loading process of a pyrotechnic composition have to be easy and applicable to a mass production. Technological process of pyrotechnic composition manufacturing Raw materials acceptance Pyrotechnic composition preparation Pyrotechnic Composition Loading Pyrotechnic System Acceptance Components preparation Mixing the components Finishing up the composition Figura 1.1 The diagram for a pyrotechnic composition manufacture process 2. CHEMICAL COMPONENTS AND DESIGN PRINCIPLES Pyrotechnic compositions are mechanical mixed compositions of two or more components which are in direct contact, and are capable to react and release a large quantity of energy and reaction products, able to generate a pyrotechnic effect".

6 There are so many chemical formulations for pyrotechnic compositions. Any attempts to classify or to simplify are always subjective. But, we can state that a pyrotechnic composition may contain the following components: Oxidants; Carburant / Fuels; Binders; Other components. Oxidants have the role to generate the oxygen or another similar element (Cl, F) that are necessary for the combustion reaction. In some pyrotechnic compositions, the oxygen isn t necessary because the air contains oxygen. This is the exception for some incendiary formulations. Carburant (often named fuel) is the indispensible component for a pyrotechnic composition. The heat released during the combustion process and the chemical composition of the reaction products determines the pyrotechnic effect. In order to ensure the homogeneity but also the geometrical configuration of a pyrotechnic charge it is necessary to introduce the binders. Every specific pyrotechnic device has a destination: illuminating, tracing, incendiary, signaling, decoy, screening etc. It is necessary in some situation to increase or decrease the combustion rate or the sensibility to external stimuli. Therefore others components are necessary for pyrotechnic compositions: Moderators / accelerators of combustion reaction; Sensitizer / Inhibitors; Stabilizers; Flames coloring components; Smoke components; Technological components. 2.1 Oxidants Every pyrotechnic composition must contain an oxidant and a carburant / fuel. The most used oxidants are: KNO 3, KClO 3, Sr(NO) 3 etc. In some cases chlorine or fluorine components are also used: CCl 4, C 2 Cl 6, C 6 Cl 6, NaFl. As an example the combustion reaction for a smoke composition can be written as following: CCl 4 2 Zn C 2 Zn Cl 2 In this case carbon tetrachloride is the oxidant (comburant in french). The selection of the oxidant (s) for a specific pyrotechnic composition is very important. The oxidant determines the chemical stability, sensibility, performance and other characteristics for the mixture. It can t be ignored that a specific role for a pyrotechnic composition means a specific chemical composition for the reaction products. As an example in order to get a red flame it is necessary to obtain in addition to the reaction products SrO / SrCl as well. In this case it s a must to use an oxidant which contains Sr, so we will use SrCO3 / Sr(NO)3.

7 It is also important to know that the oxidant determines the reaction rate and other physical, chemical and thermodynamical properties.. In pyrotechnic compositions the oxidant can be: - Salts; a. nitrates: Ba(NO 3 ) 2, Sr(NO 3 ) 2, KNO 3, NaNO 3 ; b. chlorates: KClO 3, Ba(ClO 3 ) 2 ; c. perchlorates: KClO 4, NH 4 ClO 4 ; - Peroxides: BaO 2, PbO 2 ; - Oxides; a. iron oxides: Fe 3 O 4, Fe 2 O 3 ; b. manganese oxides: MnO 2 ; c. lead oxides: Pb 3 O 4. The following oxidants can also be used: Na 2 SO 4, CaSO 4, BaSO 4, BaCrO 4, PbCrO 4, K 2 Cr 2 O 7, NaClO 4, NH 4 NO 3, PbO 2, SrO 2, SiO 2, CuO etc. Physical, chemical, and other properties for the most used oxidants are presented in table 1. Where: T T - melting temperature; T F - boiling temperature; Q F - oxidant heat of formation; Q P - heat of formation of reaction decomposition products; Q R heat of decomposition reaction; M OX/100 oxygen mass (g) released by 100 g oxidant decomposition; M OX - oxidant mass (g) which releases 1 g oxygen.

8 No. Chemical formulation Table 2.2 Oxidants properties M g/mol T T [ 0 C] Decomposition reaction Q R Q P kcal/g kcal/g g/cm 3 kcal/mol kcal/kg kcal/mol kcal/kg 1. Ba(NO 3 ) Ba(NO 3 ) 2 BaO N 2 2.5O NaNO NaNO 3 Na 2 O N 2 2.5O KNO KNO 3 K 2 O N 2 2.5O NH 4 NO NH 4 NO 3 4H 2 O 2N 2 O NH 4 NO 3 2H 2 N 2 1.5O Sr(NO 3 ) Sr(NO 3 ) 2 SrO N 2 2.5O Ca(NO 3 ) Ca(NO 3 ) 2 CaO N 2 2.5O Pb(NO 3 ) Pb(NO 3 ) 2 PbO N 2 2.5O NaNO NaNO 2 Na 2 O N 2 1.5O KClO KClO 3 KCl 1.5O NH 4 ClO NH 4 ClO 4 6H 2 O4HCl2N 2 5O KClO * KClO 4 KCl 2 O Sr(ClO 3 ) Sr(ClO 3 ) 2 SrCl 2 3 O Ba(ClO 3 ) Ba(ClO 3 ) 2 BaCl 2 3 O KMnO KMnO 4 K 2 O 2MnO 2.5O Na 2 CrO Na 2 CrO 4 2Na 2 O Cr 2 O 3 1.5O K 2 CrO K 2 CrO 4 2K 2 O Cr 2 O 3 1.5O Na 2 Cr 2 O Na 2 Cr 2 O 7 Na 2 O Cr 2 O 3 1.5O K 2 Cr 2 O K 2 Cr 2 O 7 K 2 O Cr 2 O 3 1.5O PbO PbO 2 PbO 0.5O MnO MnO 2 MnO 0.5 O MnO 2 Mn O BaO BaO 2 BaO 0.5 O BaO 2 Ba O Fe 3 O Fe 3 O 4 3Fe + 2O M OX/100 g M OX g Qf Hf

9 2.2 Fuels The fuel is an indispensable component to a pyrotechnic composition. It s impossible to have combustion without a fuel. Moreover, the desired pyrotechnic effect imposes the nature of reaction products, the amount of reaction heat, the combustion temperature, or the combustion rate How to select a fuel component When we make the choice for fuel compound we must consider all the requirements imposed for the component to achieve the pyrotechnic effect. For illuminating compositions or signaling, optimal effect is achieved to a higher combustion temperature. So it is important to use only a high caloric compound. For colored signaling smokes a high combustion temperature is not allowed because it can destroy the colorants. When we select the carburant it is important to know the oxidation reaction products and their properties. Figure 2. CuCl Emission spectrum The fuels used in pyrotechnic compositions must satisfy the following requirements: To release a sufficient thermical effect; To be easily oxidized; To release the specific oxidation products; To be chemically and physically stable between 50 0 C 60 0 C; To be non hygroscopic; To be easily processed / grinded; To be non toxic; To be available. There are different types of carburants: A. Inorganic fuels: a) metals: magnesium (Mg), aluminum (Al), zinc (Zn) etc.; b) metallic alloys: aluminum-magnesium (AM), silicium aluminum etc.; c) metalloid: phosphorus (P), sulfur (S), carbon (C); d) sulfides: phosphorus trisulphide (P 4 S 3 ), antimony sulfide (Sb 2 S 3 ); e) other substances: calcium silicide (CaSi 2 ). B. Organic fuels a) hydrocarbons from aliphatic series: gasoline, kerosene, benzene, oil; b) carbohydrates: starch, lactose, sucrose, cellulose; c) other organic substances.

10 Table 2 Fuels, oxides and heat of formation Combustible Oxides Heat of formation [kcal/mole] Symbol A M Formulas [g] [g/mol] Q f OXIDE Q 1 = Q f /ma Q 2 = Q f /M Q 3 = Q f /n Be 9.0 BeO Al 27.0 Al 2 O B 10.8 B 2 O Li 6.9 Li 2 O H 1.0 H 2 O Mg 24.3 MgO Ca 40.1 CaO Si 28.1 SiO Ti 47.9 TiO V 51.0 V 2 O P 31.0 P 2 O C 12.0 CO Zr 91.2 ZrO Na 23.0 Na 2 O K 39.1 K 2 O Sr 87.6 SrO Ba BaO Zn 65.4 ZnO Ce CeO Hf HfO Th ThO As 74.9 As 2 O Sb Sb 2 O S 32.1 SO Se 79.0 SeO Cr 52.0 Cr 2 O Mn 54.9 MnO Fe 55.8 Fe 2 O

11 3 Green pyrotechnic compositions and their applications The use of pyrotechnics extends well beyond fireworks, with common applications in airbags, road flares, and fire extinguishers. Perhaps the most common use of pyrotechnics, though possibly overlooked by the general public, is by the militaries of the world. Military pyrotechnics encompasses many areas, including, but not limited to, illuminating charges, smokes for obscuration and signaling, delay fuzes, incendiary devices, countermeasure flares, and primers. On the battlefield and on training ranges, the area of pyrotechnics surrounds the warfighter, and in many cases, the proper and consistent functioning of a pyrotechnic can be the difference between life and death Historically, when the toxicity of chemicals was not known and when regulations were relatively few in number, many pyrotechnic formulations were designed primarily to function reliably. Many of these historic formulations in the aforementioned areas are still being used today because they have already been proven-out, consistently pass quality control tests, and function very well in a wide range of temperatures. Today, however, more is known concerning the toxicity profile of chemicals found in these historic pyrotechnic formulations. Some chemicals found in these pyrotechnic formulations are no longer viewed as being acceptable due to their environmental and occupational health hazards alike. As the toxicity profiles of pyrotechnic chemicals have become known, governments at the federal and state levels in the United States have called for increased regulations of these chemicals to address environmental issues and human health concerns. Due to the increased regulations and supposed toxicities of many traditional pyrotechnic chemicals, the abilities of military personnel to train on training ranges within or outside the continental United States has been hampered or prohibited. Because commercial fireworks companies in the United States are also coming under increasing scrutiny to green their fireworks, any technological breakthroughs made to generate environmentally sustainable pyrotechnics without compromising human health may also spur interest from the commercial fireworks sectors. Although there is a significant interest in the development of green technologies for military and civilian pyrotechnics, these technologies will be of limited or no value if the performances and safeties of these new pyrotechnic formulations are compromised. Therefore, green pyrotechnic formulations should consist of environmentally acceptable ingredients, have equal or enhanced performances, and have identical or reduced sensitivities to ignition stimuli (i.e., impact, friction, and electrostatic discharge) compared to the environmentally questionable pyrotechnic munitions that are in existence today.