Ammonium perchlorates

Ammonium perchlorate (AP NH4CIO4) is a white, crystalline material, the crystal structure of which changes from orthorhombic to cubic at 513 K, which affects the decomposition process. AP is not hygroscopic in the atmosphere and the mass fraction of oxygen is 0.545. It is used as an oxidizer in various types of propellants and pyrolants. A rapid sublimation occurs between 670 K and 710 K at low pressures. Under slow heating, AP starts to decompose at about 470 K according to  

2NH4CIO4 CI2 + O2 + 4H2O + 2NO When the heahng rate is high, the overall reaction process is NH4CIO4 NH3 + HCIO4 

This reaction is exothermic and produces excess oxygen as an oxidizer. 

The oxygen molecules produced by the decomposition act as an oxidizer when AP particles are mixed with a polymeric fuel component, for example  

This reaction produces significant amounts of heat and gaseous molecules, which yield a high fp as defined in Eq. (1.76). 

AMMONIUM SALTS CONTAINING OXYANIONS OF THE NON-METALS 4.1.1 Ammonium perchlorate 

The thermal reactions of ammonium perchlorate (AP) are unusually complicated. On account of the importance of this compound as a solid propellant and also its intrinsic interest, an intensive and widespread series of studies has been completed using various experimental approaches. The main kinetic characteristics of the reactions involved and the mechanistic explanations of these observations are largely agreed. There have been two detailed reviews of the literature to mid-1968 [59,357]. 

Microscopic examination has shown [102,922] that the compact nuclei, comprised of residual material [211], grow in three dimensions and that the rate of interface advance with time is constant [922]. These observations are important in interpreting the geometric significance of the obedience to the Avrami—Erofe ev equation [eqn. (6)] [59,923]. The rate of the low temperature decomposition of AP is influenced by the particle ageing [924] and irradiation [45], the presence of gaseous products [924], ammonia [120], perchloric acid [120] and additives [59]. 

The first step in the low temperature reaction of AP is proton transfer [46,59,915,925—930] 

This explains the increase in the induction period which is apparent after exposure of the salt to ammonia, and the decrease in the induction period found for samples which contain traces of HCIO4, identified as the unstable species [59,925]. In the low temperature range, the presence of an outer layer of adsorbed NH3 and/or NH4 ions suppresses the formation of HC104 and, in consequence, the decomposition reaction. 

The explosive salts of perchloric acid are considerably more interesting than the explosive chlorates, since these are more stable and safer to handle. A few of them, for instance ammonium perchlorate, rank as components of explosive mixtures and rocket propellants. Some salts of perchloric acid possess initiating properties (Vol. III). 

Others, for instance guanidine perchlorate, pyridine perchlorate, are among the strongest explosives. 

Potassium perchlorate, a non-explosive compound, is an important ingredient in many mixed explosives. An excellent monograph on perchlorates was written by Schumacher [54], 

There exist two crystalline modifications of ammonium perchlorate, NH4C104 an orthorhombic form below 240°C, and a cubic form above this point. An addition of small amount of some dyestuffs inhibits change of the crystalline forms [52]. 

The explosive properties of ammonium perchlorate are more marked than those of ammonium nitrate. 

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If this electrostatic treatment of the substituent effect of poles is sound, the effect of a pole upon the Gibbs function of activation at a particular position should be inversely proportional to the effective dielectric constant, and the longer the methylene chain the more closely should the effective dielectric constant approach the dielectric constant of the medium. Surprisingly, competitive nitrations of phenpropyl trimethyl ammonium perchlorate and benzene in acetic anhydride and tri-fluoroacetic acid showed the relative rate not to decrease markedly with the dielectric constant of the solvent. It was suggested that the expected decrease in reactivity of the cation was obscured by the faster nitration of ion pairs. 

Ammonium perchlorate Hot copper tubing, sugar, flnely divided organic or combustible materials, potassium periodate and permanganate, powdered metals, carbon, sulfur... 

Relatively iasensitive explosives of medium energy levels have also been formulated usiag propeUant-type formulations containing ammonium perchlorate, aluminum, and a polybutadiene or polyester biader (267—270). 

Polymer-based rocket propellants are generally referred to as composite propellants, and often identified by the elastomer used, eg, urethane propellants or carboxy- (CTPB) or hydroxy- (HTPB) terrninated polybutadiene propellants. The cross-linked polymers act as a viscoelastic matrix to provide mechanical strength, and as a fuel to react with the oxidizers present. Ammonium perchlorate and ammonium nitrate are the most common oxidizers used nitramines such as HMX or RDX may be added to react with the fuels and increase the impulse produced. Many other substances may be added including metallic fuels, plasticizers, stabilizers, catalysts, ballistic modifiers, and bonding agents. Typical components are Hsted in Table 1. 

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. 

Pollution Prevention. Procedures haven been developed for recovery of composite ammonium perchlorate propellant from rocket motors, and the treatment of scrap and recovered propellant to reclaim ingredients. These include the use of high pressure water jets or compounds such as ammonia, which form fluids under pressure at elevated temperature, to remove the propellant from the motor, extraction of the ammonium perchlorate with solvents such as water or ammonia as a critical fluid, recrystalli2ation of the perchlorate and reuse in composite propellant or in slurry explosives or conversion to perchloric acid (166,167). 

R. H. Waesche, "Workshop in the Relationship of Ammonium Perchlorate Decomposition to Dedagration," Proceedings of the 7th JMNNMF Combustion Meeting, Vol. 1, CPIA Pubhcation 204, CPIA, Johns Hopkins University, Laurel, Md., 1971, p. 15. 

The most outstanding property of the perchlorates is their oxidising abiUty. On heating, these compounds decompose into chlorine, chlorides, and oxygen gas. Aqueous perchlorate solutions exhibit Httle or no oxidising power when dilute or cold. However, hot concentrated perchloric acid is a powerful oxidizer and whenever it contacts oxidizable matter extreme caution is required. The acidified concentrated solutions of perchlorate salts must also be handled with caution. Ammonium perchlorate [7790-98-9] (AP) is one of the most important perchlorates owing to its high (54.5%) O2 content and the... 

Perchloric acid can be prepared by the treatment of perchlorates with sulfuric acid followed by distillation. A modification of the procedure (21) involves the reaction of ammonium perchlorate with nitric and hydrochloric acids, and then concentration at 198—200°C to eliminate the unreacted acids by vacuum distillation ... 

Ammonium Perchlorate. Heats of formation for the metal perchlorates are nearly the same as those for the corresponding chlorides, so that the reaction... 

Ammonium perchlorate is a colorless, crystalline compound having a density of 1.95 g/mL and a molecular weight of 117.5. It is prepared by a double displacement reaction between sodium perchlorate and ammonium chloride, and is crystallized from water as the anhydrous salt. 

Because of the use of ammonium perchlorate as a soHd oxidizer for rocket propeUants, the thermal decomposition has been much studied (29—32). Three separate activation energies have been observed for AP decompositions an activation energy of 123.8 kJ/mol (29.6 kcal/mol) is found below 240°C of 79.1 kj/mol (18.9 kcal/mol) above 240°C and finally, of 307.1 kj/mol (73.4 kcal/mol) between 400—440°C (33,34). Below 300°C, the equation... 

The ammonium perchlorate solution is spray-dried to the desired crystal size at air temperatures below 150°C and crystal temperatures of about 110°C. This procedure provides a pure product having a controlled grain size. Prior mechanical and thermal treatment affects the isothermal... 

Alkali Metal Perchlorates. The anhydrous salts of the Group 1 (lA) or alkah metal perchlorates are isomorphous with one another as well as with ammonium perchlorate. Crystal stmctures have been determined by optical and x-ray methods (38). With the exception of lithium perchlorate, the compounds all exhibit dimorphism when undergoing transitions from rhombic to cubic forms at characteristic temperatures (33,34). Potassium perchlorate [7778-74-7] KCIO, the first such compound discovered, is used in pyrotechnics (qv) and has the highest percentage of oxygen (60.1%). 

Ammonium Perchlorate. The commercial AP product is manufactured by the double-exchange reaction of sodium perchlorate and ammonium chloride (102,103). 

Ammonia, hydrochloric acid, and sodium perchlorate are mixed and the reaction mixture crystallised in a vacuum-cooled crystalliser. Ammonium perchlorate crystals are centrifuged, reslurried, recentrifuged, and then dried and blended for shipment. Mother Hquor is evaporated to precipitate sodium chloride and the depleted mother Hquor is recycled to the reactor. The AP product made by this method is 99% pure and meets the specifications for propeUant-grade ammonium perchlorate. The impurities are ammonium chloride, sodium perchlorate, ammonium chlorate, and water insolubles. 

Extremely high purity ammonium perchlorate can be made by the direct reaction of ammonia and pure perchloric acid solution (8,36) ... 

The U.S. domestic capacity of ammonium perchlorate is roughly estimated at 31,250 t/yr. The actual production varies, based on the requirements for soHd propellants. The 1994 production ran at about 11,200 t/yr, 36% of name plate capacity. Environmental effects of the decomposition products, which result from using soHd rocket motors based on ammonium perchlorate-containing propellants, are expected to keep increasing pubHc pressure until consumption is reduced and alternatives are developed. The 1995 price of ammonium perchlorate is in the range of 1.05/kg. Approximately 450 t/yr of NH ClO -equivalent cell Hquor is sold to produce magnesium and lithium perchlorate for use in the production of batteries (113). Total U.S. domestic sales and exports for sodium perchlorate are about 900 t/yr. In 1995, a solution containing 64% NaClO was priced at ca 1.00/kg dry product was also available at 1.21/kg. 

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. 

Most of the NaClO produced is converted to ammonium perchlorate [7790-98-9] NH CIO. ... 

The products of equation 11 are separated by controlled crystalLi2ations to produce high purity crystalline anhydrous ammonium perchlorate and sodium chloride. The main use for ammonium perchlorate is as an oxidi2er in the propellant of rockets and missiles (see Explosives and propellants). 

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