Decomposition rate ammonium perchlorate

Varying the semiconducting properties of the catalyst crystal affects the rate of ammonium perchlorate decomposition. 

Accumulatory pressure measurements have been used to study the kinetics of more complicated reactions. In the low temperature decomposition of ammonium perchlorate, the rate measurements depend on the constancy of composition of the non-condensable components of the product mixture [120], The kinetics of the high temperature decomposition [ 59] of this compound have been studied by accumulatory pressure measurements in the presence of an inert gas to suppress sublimation of the solid reactant. Reversible dissociations are not, however, appropriately studied in a closed system, where product readsorption and diffusion effects within the product layer may control, or exert perceptible influence on, the rate of gas release [121]. 

J.R. Ward J J. Rocchio, Effect of Neutron Radiation on the Rate of Ammonium Perchlorate Decomposition Reactions Involved in Combustion , Ibid, paper 6.4, pp 271—80 (1975) 246) Ibid, Effect of Neutron Radia-... 

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. 

Catalysts which enhance the burning rate of composite propellants are generally believed to accelerate the decomposition of ammonium perchlorate, but the catalytic mechanism is still not very clear. The important observed aspects of this catalysis can be summarized as follows ... 

Horton (H9, H10) has obtained additional acoustic-admittance data for a series of composite propellants. At a given frequency, decreasing the mean oxidizer particle size increases the acoustic admittance and thereby the tendency for instability. Horton also investigated the effects on the acoustic admittance of the incorporation of traces of copper chromite, a known catalyst, for the decomposition of ammonium perchlorate, lithium fluoride (a burning-rate depressant), and changes in binder these data are difficult to analyze because of experimental errors. 

Some limitations of optical microscopy were apparent in applying [247—249] the technique to supplement kinetic investigations of the low temperature decomposition of ammonium perchlorate (AP), a particularly extensively studied solid phase rate process [59]. The porous residue is opaque. Scanning electron microscopy showed that decomposition was initiated at active sites scattered across surfaces and reaction resulted in the formation of square holes on m-faces and rhombic holes on c-faces. These sites of nucleation were identified [211] as points of intersection of line dislocations with an external boundary face and the kinetic implications of the observed mode of nucleation and growth have been discussed [211]. 

The Avrami—Erofe ev equation, eqn. (6), has been successfully used in kinetic analyses of many solid phase decomposition reactions examples are given in Chaps. 4 and 5. For no substance, however, has this expression been more comprehensively applied than in the decomposition of ammonium perchlorate. The value of n for the low temperature reaction of large crystals [268] is reduced at a 0.2 from 4 to 3, corresponding to the completion of nucleation. More recently, the same rate process has been the subject of a particularly detailed and rigorous re-analysis by Jacobs and Ng [452] who used a computer to optimize curve fitting. The main reaction (0.01 < a < 1.0) was well described by the exact Avrami equation, eqn. (4), and kinetic interpretation also included an examination of the rates of development and of multiplication of nuclei during the induction period (a < 0.01). The complete kinetic expressions required to describe quantitatively the overall reaction required a total of ten parameters. 

Fig. 176. Rate of decomposition of ammonium perchlorate. Variation with temperature according to Bircumshaw and Newman [5],...

Al Fakir, M. S., Progr. Astronaut. Aeronaut., 1981, 76, 5512—564 Admixture of lithium perchlorate [1] or zinc perchlorate [2] leads to decomposition with explosion at 290° or ignition at 240°C, respectively. The role of ammine derivatives of lithium and magnesium perchlorates in catalysing the thermal decomposition of ammonium perchlorate has been studied [3], and lithium perchlorate has a strong catalytic effect on the burning rate [4]. 

The perchlorate was found to sublime in vacuo to some extent at all temperatures. A small pressure of inert gas was found to reduce the sublimation. The sublimate was foimd to be ammonium perchlorate with traces of H and NOf ions. It decomposed with a reduced induction period at a slightly higher rate. It was found that sublimation continued after decomposition had stopped. It is curious that the vapour, which may or may not be dissociated, is not decomposed at these temperatures. 

EXPLOSION and FIRE CONCERNS combustible solid flammable moderate fire risk NFPArating (not rated) volatile in steam contact with strong oxidizing agents may cause fires and explosions violent reaction with ammonium perchlorate incompatible with tetrani-tromethane and mercury (II) nitrate thermal decomposition may generate carbon monoxide and carbon dioxide use alcohol foam, water spray, dry chemical powder, or carbon dioxide for fire fighting purposes. 

The growth of the decomposition reactions to burning or detonation has not been studied with the intensity devoted to the initiation of reaction. The speed of the transition and the rate of detonation in azides make detailed studies difficult deflagration has been studied more commonly with slower-burning substances such as ammonium perchlorate. 

Baumgartner et al. (9) compared the thermal and mechanical degradation of filled and unfilled elastomers. They were particularly interested in the long-term aging and fatigue behavior of solid propellants filled with ammonium perchlorate or potassium chloride. They reported that the mechanisms for thermally and mechanically induced decomposition of the propellant binder appear equivalent. At low temperatures, mechanical processes control the decomposition rates of the polymers, whereas thermal processes control the decomposition at high temperature. They further note that, "Equivalence of thermal and mechanical degradation... 

Oxidizers such as ammonium perchlorate, chlorates, and periodates have been exposed to UV radiation, and in many cases chemical activity and decomposition rates could be increased. The pre-irradiation of ammonium perchlorate has been studied by Freeman and Anderson, the decomposition of potassium periodate by Phillips and Taylor,and NavOrd 7147 quotes several authors in connection with work on chlorates. A growing literature in this special field is to be expected and present interest is indicated in several articles in the book Reactivity of SoIidsJ ... 

Ammonium perchlorate is the primary oxidizer used for solid rocket propellant formulations, in large part because of its gas-generating capabilities. Ammonium perchlorate has been shown to be capable of catalytic decomposition, with metal oxides such as iron(III) oxide the most commonly used materials. A low percentage of catalyst added to a propellant formulation can produce a significant increase in propellant burn rate. 

The iron oxide serves as a bum rate catalyst, speeding up the thermal decomposition of the ammonium perchlorate. Other metal oxides have been shown to also display catalytic effects with AP. Little use of catalysts is otherwise seen with pyrotechnic-type compositions, where the goal is to control, rather than maximize, bum rate. 

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