Ammonium perchlorate flames

Fig. 1. The postulated flame stmcture for an AP composite propellant, showing A, the primary flame, where gases are from AP decomposition and fuel pyrolysis, the temperature is presumably the propellant flame temperature, and heat transfer is three-dimensional followed by B, the final diffusion flame, where gases are O2 from the AP flame reacting with products from fuel pyrolysis, the temperature is the propellant flame temperature, and heat transfer is three-dimensional and C, the AP monopropellant flame where gases are products from the AP surface decomposition, the temperature is the adiabatic flame temperature for pure AP, and heat transfer is approximately one-dimensional. AP = ammonium perchlorate.

Oxidizers. The characteristics of the oxidizer affect the baUistic and mechanical properties of a composite propellant as well as the processibihty. Oxidizers are selected to provide the best combination of available oxygen, high density, low heat of formation, and maximum gas volume in reaction with binders. Increases in oxidizer content increase the density, the adiabatic flame temperature, and the specific impulse of a propellant up to a maximum. The most commonly used inorganic oxidizer in both composite and nitroceUulose-based rocket propellant is ammonium perchlorate. The primary combustion products of an ammonium perchlorate propellant and a polymeric binder containing C, H, and O are CO2, H2, O2, and HCl. Ammonium nitrate has been used in slow burning propellants, and where a smokeless exhaust is requited. Nitramines such as RDX and HMX have also been used where maximum energy is essential. 

Pyrotechnic mixtures may also contain additional components that are added to modify the bum rate, enhance the pyrotechnic effect, or serve as a binder to maintain the homogeneity of the blended mixture and provide mechanical strength when the composition is pressed or consoHdated into a tube or other container. These additional components may also function as oxidizers or fuels in the composition, and it can be anticipated that the heat output, bum rate, and ignition sensitivity may all be affected by the addition of another component to a pyrotechnic composition. An example of an additional component is the use of a catalyst, such as iron oxide, to enhance the decomposition rate of ammonium perchlorate. Diatomaceous earth or coarse sawdust may be used to slow up the bum rate of a composition, or magnesium carbonate (an acid neutralizer) may be added to help stabilize mixtures that contain an acid-sensitive component such as potassium chlorate. Binders include such materials as dextrin (partially hydrolyzed starch), various gums, and assorted polymers such as poly(vinyl alcohol), epoxies, and polyesters. Polybutadiene mbber binders are widely used as fuels and binders in the soHd propellant industry. The production of colored flames is enhanced by the presence of chlorine atoms in the pyrotechnic flame, so chlorine donors such as poly(vinyl chloride) or chlorinated mbber are often added to color-producing compositions, where they also serve as fuels. 

Ammonia (see also under ammonium perchlorate). Perchloric ac vapor and anhyd ammonia were reacted in a countercurrent flow reactor with the object of obtaining a stable flame. The vapors were found to react vigorously with the formn of gaseous prods and copious deposits of amm chloride, but a stable flame could not be established (Ref 39)... 

The burning mechanism of composite propellants differs from that described above. There is no exothermic reaction which can lead to a self-sustaining fizz zone. Instead, the first process appears to be the softening and breakdown of the organic binder/fuel which surrounds the ammonium perchlorate particles. Particles of propellant become detached and enter the flame. The binder is pyrolysed and the ammonium perchlorate broken down, initially to ammonia and perchloric acid. The main chemical reaction is thus in the gas phase, between the initial dissociation products. 

When a composite propellant composed of ammonium perchlorate (AP) and a hydrocarbon polymer burns in a rocket motor, HCl, CO2, H2O, and N2 are the major combustion products and small amounts of radicals such as OH, H, and CH are also formed. These products are smokeless in nature and the formation of carbon particles is not seen. The exhaust plume emits weak visible light, but no afterburning occurs because AP composite propellants are stoichiometrically balanced mixtures and, in general, no diffusional flames are generated. 

Mixtures of ammonium perchlorate with fuels can produce high temperatures when ignited, and the hydrogen chloride (HCl) liberated during the reaction can aid in the production of colors. These two factors make ammonium perchlorate a good oxidizer for colored flame compositions (see Chapter 7). 

Ammonium perchlorate (NH ClO ) This is a good oxidizer, and can be used to make excellent propellants and colored flames. However, it is a self-contained oxidizer-fuel system (much like ammonium nitrate). The mixing of NH f (fuel) and ClOa (oxidizer) occurs at the ionic level. The potential for an explosion cannot be ignored. Conclusion if this material is used, it must be treated with respect and minimum quantities of bulk powder should be prepared. 

Price, "Contrasting Patterns in the Behavior of High Explosives , llthSympCombstn (1967), p 695, Fig 4, which shows that for Group 2 explosives deton vel at first increases with density, then it falls, and finally the detonation fails) 10) D. Price et al, "Explosive Behavior of Ammonium Perchlorate , Combustion Flame 11, p 419, Figs 5 6 (1967) (Detonation velocity vs density of AP curves show that increase of density above critical values results in failures)... 

D. Price et al, "Explosive Behavior of Ammonium Perchlorate , Combustion 8t Flame 11, 415-25 (Oct 1967) 16) C.G. Dunkle, private... 

Figure 24. Composition diagram of chamber flame temperature, °F., for ammonium perchlorate-aluminum-polybutadiene/BITA propellant. Pc = 1000 p.s.i.a. shifting equilibrium...

Ammonium perchlorate is a monopropellant which is exothermic in its decomposition to the extent of 270 cal./gram (1, 30, 54), based on measured decomposition products, and has a measured adiabatic flame temperature of 950°C. (1, 54) (see Table I). The dissociative sublimation step is zero order and is endothermic to the extent of 500 cal./gram... 

Figure 1. Two-stage granular diffusion flame model for ammonium perchlorate-type composite solid propellants...

W.A. Rosser, S.H. Inami, H. Wise, Thermal Decomposition of Ammonium Perchlorate, Combust. Flame, 12 (1968) 427-435. 

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