Rocket propellants properties

Rocket Propellants. SoHd rocket propellants are mostly based on chemically cross-linked polymeric elastomers to provide the mechanical properties required in launchings and the environmental conditions experienced in storage, shipment, and handling (see Elastomers, synthetic). Double-and triple-based nitrocellulose propellants are also employed as rocket propellants. 

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. 

Solventless Extrusion Process. The solvendess process for making double-base propellants has been used ia the United States primarily for the manufacture of rocket propellant grains having web thickness from ca 1.35 to 15 cm and for thin-sheet mortar (M8) propellant. The process offers such advantages as minimal dimensional changes after extmsion, the elimination of the drying process, and better long-term baUistic uniformity because there is no loss of volatile solvent. The composition and properties of typical double-base solvent extmded rocket and mortar propellant are Hsted ia Table... 

Oxidizing Properties. Nitric acid is a powerful oxidizing agent (electron acceptor) that reacts violentiy with many organic materials (eg, turpentine, charcoal, and charred sawdust) (19,20). The concentrated acid may react explosively with ethanol (qv). Such oxidizing properties have had military appHcation nitric acid is used with certain organics, eg, furfuryl alcohol and aniline, as rocket propellant (see Explosives AND PROPELLANTS). 

Double-base propellants containing azide polymers are termed nitro-azide polymer propellants. DEP used as a plasticizer of double-base propellants is replaced with azide polymers in order to increase energy density. The compatibility of GAP prepolymer with NG serves to suitably desensitize the mechanical sensitivity of NG and gives superior mechanical properties in the formulation of rocket propellant grains. 

Similar to nitramine composite propellants and TAGN composite propellants, AN composite propellants produce halogen-free combustion products and thus represent smokeless propellants. However, their ballistic properties are inferior to those of other composite propellants the burning rate is too low and the pressure exponent is too high to permit fabrication of rocket propellant grains. In addition, the mechanical properties of AN composite propellants vary with temperature due to the phase transitions of AN particles. 

When HNF or ADN particles are mixed with a GAP copolymer containing aluminum particles, HNF-GAP and ADN-GAP composite propellants are formed, respectively. A higher theoretical specific impulse is obtained as compared to those of aluminized AP-HTPB composite propellants.However, the ballistic properties of ADN, HNIW, and HNF composite propellants, such as pressure exponent, temperature sensitivity, combustion instability, and mechanical properties, still need to be improved if they are to be used as rocket propellants. 

Hydrocellulose differs from hydrated cellulose in its properties (Ref 3). According to Stettbacher (Ref 5) hydrocellulose lies between the hydrated cellulose and oxycellulose. Its use as a flash reducer in a propellant has been claimed by C.R. Franklin in USP 1564549 (1925) CA 20, 505 (1926). Accdg to CIOS Rept 31-68 (1945), pp 6-7, hydrocellulose was used during WWII by Germans in some rocket propellants, presumably to improve their burning characteristics. For instance the so-called Ammon-pulver contained 5% hydrocellulose and the EP (Einheitspulver) contained about 3%. Hydrocellulose was also used in some rocket propellants to increase the rate of burning at low temperature... 

In the simple two-component system of PVC binder and oxidizer, the important propellant properties of specific impulse, density, adiabatic flame temperature, and burning rate increase with an increase in solids loading. This is shown in Figure 8, where theoretical calculated values of specific impulse, adiabatic flame temperature, and density are given for a range of oxidizer content for PVC plastisol propellants comprised of only binder and oxidizer. [Calculated values of specific impulse reported throughout this paper are for adiabatic combustion at a rocket chamber pressure of 1000 p.s.i.a. followed by isentropic expansion to 1 atm. pressure with the assumptions that during the expansion process chemical compo-... 

A much larger number of new molecules were synthesized whose properties were found to be unacceptable for use in rocket engines. Many were rejected because they had unsuitable energy, others had poor densities, viscosities, or vapor pressures and still others were too reactive, unstable, or detonable. The remainder of this paper will deal with the methods used to determine the properties which determine whether or not a new material could be used as a rocket propellant. 

Specific impulse (Isp) is the most important single ballistic property for rocket propellants and its value is of utmost significance for the determination of propel-... 

BAMO is perhaps the most prominent among the azido oxetanes class in terms of the number of polymers and copolymers reported so far. Due to its symmetrical azido groups, it assumes special significance as a hard block repeating unit in a thermoplastic elastomer. However, the homopolymer is solid and cannot be used directly for binder applications because of its crystal-tine nature. Also, poly(BAMO) shows relatively poor mechanical properties as a binder for solid rocket propellants [153]. Many copolymers of BAMO with non-energetic co-monomers tike tetrahydrofuran (THF) have been reported. The BAMO-THF copolymer is an excellent candidate for binder applications with its energetic BAMO content coupled with the THF block which affords... 

Hamilton and coworkers designed a rocket propellant formulation based on BAMO-AMMO Copolymer TPE and 80% total solids (AP and Al) and it was directly cast into a phenolic case and required no liner or insulation. The results of firing of a 18 kg test motor exhibited completely acceptable ballistic properties. The authors claimed it to be the 1st demonstration of a high energy TPE motor firing [158]. Prior to this, Wardle and his team reported BAMO-AMMO copolymer and CL-20-based potentially attractive high energy ETPE gun propellants. 

NENAs possess good thermal stability, readily plasticize NC and other binders, generate low molecular weight combustion products and impart favorable impact sensitivity. Butyl NENA has edge over others because it imparts better low temperature properties as well [182]. The use of NENAs as plasticizers in gun and rocket propellant formulations imparts excellent properties such as high bum rates, reduction in flame temperature and molecular mass of combustion products and high force constant or specific impulse [183]. 

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