Oxidizers, propellant ammonium nitrate

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. 

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. 

Characteristics of common inorganic oxidizers are Hsted in Table 5. In any homologous series, potassium perchlorate-containing propellants bum fastest ammonium nitrate propellants bum slowest (79,80). 

Industrial. Nitric acid is itself the starting material for ammonium nitrate, nitroglycerin [55-63-0] trinitrotoluene [118-96-7]., nitroceUulose [9004-70-0] and other nitrogen compounds used in the manufacture of explosives (see Explosives and propellants). Nitric acid is made by oxidation of ammonia to nitrogen dioxide [10102-44-0] which is subsequently absorbed by water. 

A small but important use of ammonium nitrate is in the production of nitrous oxide during the 1980s consumption for this purpose averaged about 30,000 t. The gas is generated by controlled heating of ammonium nitrate above 200°C. Nitrous oxide is used primarily as an anesthetic and as an aerosol propellant for food products (see Anesthetics Aerosols). 

WEB Dinitrogen oxide, commonly called nitrous oxide, is used as a propellant gas for whipped-cream dispensers. It is prepared by heating ammonium nitrate to 250°C Water vapor is also formed. 

Ammonium nitrate (AN NH4NO3) is a white, crystalline material, the crystal structure of which varies with temperature.melting point is 442 K and its heat of fusion is 71.4 kj kg . Though the mass fraction of oxygen of AN is 0.5996, it is highly hygroscopic and absorbs moisture from the atmosphere to form liquid AN acid. This limits its application in propellants and pyrolants. However, AN is widely used as an oxidizer of explosives such as slurry explosives and ANFO (ammonium nitrate fuel oil) explosives. 

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. 

The solids content of propellants ranges between 70 and 90%. The higher limit is dictated by processability. Propellants with less than 70% solids are rare since the specific impulse of such combinations is unduly low. Ammonium perchlorate is the preferred oxidizer and takes the largest percentage in the composition. For special formulations ammonium nitrate or other oxidizing agents may be encountered. Aluminum powder is the most frequently used additive to boost specific impulse and may be found in quantities up to 25%. 

A family of high performance and clean space motor/gas generators and large launch vehicle solid propellants based on poly(GlyN) binder, ammonium nitrate oxidizer and small amounts of aluminum and/or boron with optimized performance at low solids loading (without the presence of plasticizers) and also poly(GlyN) binder, ammonium nitrate oxidizer and aluminum or magnesium fuel have been reported in the literature [141, 142]. These solid propellant formulations produce essentially no HC1 or chloride ions in the exhaust and are considered eco-friendly. 

Phillips Petroleum in the United States [23] developed a propellant composed of ammonium nitrate as oxidant and rubber as a combustible and binding agent. The rubber consists of synthetic rubber and such typical rubber ingredients as carbon black (to improve the mechanical properties of rubber), an accelerator and an inhibitor (to prevent oxidation). To endow the rubber with sufficient plasticity... 

Typical propellants with ammonium nitrate as oxidizer... 

Fig. 126. Thermal layer model of combustion of solid composite propellant with ammonium nitrate, according to Chaiken [2] R—redox reaction flame zone (temperature 7f), u—gas velocity, S—thickness of the thermal layer, T —surface temperature of oxidizer particle, ro—radius of oxidizer particle.

All explosive materials contain oxygen, which is needed for the explosive reaction to take place. The oxygen can be introduced by chemical reactions (nitration) or by mechanical incorporation of materials containing bound oxygen. The most important solid-state oxidizers are nitrates, especially -> Ammonium Nitrate and -> Sodium Nitrate for explosives -> Potassium Nitrate for -> Black Powder and ion exchanged -> Permitted Explosives, potassium chlorate for -> Chlorate Explosives and for pyrotechnical compositions Ammonium Perchlorate (APC) for -> Composite Propellants. 

Ionic liquids should also be very suitable for use as monopropellants, but the salts used must contain either the oxidizer and fuel combined, or salt mixtures which contain both oxidizing and reducing salts. Since these mixtures are homogeneous systems which contain both the oxidizer and fuel, they can be labeled as monopropellants, just as hydrazine is. Particularly interesting are salt mixtures which are less toxic and have a lower vapor pressure than hydrazine. Such mixtures are also known as green propellants . Suitable anions are the nitrate or dinitramide ions [58], A combination which has already been studied intensively as an oxidizer is the HAN, hydroxylammonium nitrate system. ADN, ammonium nitrate (AN) and hydrazinium nitrate (HN) have also been investigated. As fuels, hydroxylammonium azide (HAA), ammonium azide (AA) or hydrazinium azide (HA) may be appropriate. As a rule, these salt mixtures are not used as pure substances on safety grounds, but with 20 or 40% water added they then decompose catalytically in an exothermic reaction. Table 9.7 shows the dependence of the calculated specific impulses on the water content for such salt mixtures. 

A-Nitro and acetyl-substituted 1,3,5,7-tetrazocanes are important compounds as explosives and propellants <1996CHEG-II(9)705>. In the syntheses of the nitro-substituted 1,3,5,7-tetrazocanes, their processing, and application, it is possible that they come into contact with ammonium nitrate, or they are directly mixed with this oxidant. Thermal reactivity of the nitro-substituted 1,3,5,7-tetrazocanes has been examined by means of nonisothermal differential thermal analysis <2005MI11>. It has been established that impurities of ammonium nitrate can destabilize some A-substituted 1,3,5,7-tetrazocanes and that this effect is due to acidolytic attack of nitric acid. 

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