Composite Modified Double-Base Propellants

M.C, Philpot, Gas Chromatographic Determination of Plasticizers and Stabilizers in Composite Modified Double-Base Propellants , AnalChem 41 (1), 166-8 (1969) CA 70, 49143 (1969) 49) J. Trauchant, Chromato-... 

A third type of propellant, the composite modified-double-base propellant, represents a combination of the other two types. These propellants are made from mixtures of nitroglycerine and nitrocellulose or similar materials, but with crystalline oxidizers such as ammonium perchlorate also included in the matrix. 

One extremely important point to realize is that different propellant types may have different rate-controlling processes. For example, the true double-base propellants are mixed on a molecular scale, since both fuel and oxidizing species occur on the same molecule. The mixing of ingredients and their decomposition products has already occurred and can therefore be neglected in any analysis. On the other hand, composite and composite modified-double-base propellants are not mixed to this degree, and hence mixing processes may be important in the analysis of their combustion behavior. 

CMDB Composite modified double-base (propellant)... 

Since the energetics of nitropolymer propellants composed of NC-NG or NC-TMETN are limited due to the limited concentration of oxidizer fragments, some crystalline particles are mixed within these propellants in order to increase the thermodynamic energy or specific impulse. The resulting class of propellants is termed composite-modified double-base (CMDB) propellants . The physicochemical properhes of CMDB propellants are intermediate between those of composite and double-base propellants, and these systems are widely used because of their great potential to produce a high specific impulse and their flexibility of burning rate. 

When crystalline AP particles are mixed with nitropolymers, ammonium perchlorate composite-modified double-base (AP-CMDB) propellants are formulated. A nitropolymer such as NC-NG or NC-TMETN double-base propellant acts as a... 

When nitramine particles such as HMX or RDX particles are mixed with a doublebase propellant, nitramine composite-modified double-base propellants are formulated. Since HMX and RDX are stoichiometrically balanced materials, the use of these nitramine particles leads to a somewhat different mode of combustion as compared to AP-CMDB propellants. Since each nitramine particle can burn independently of the base matrix at the burning surface, a monopropellant flamelet is formed in the gas phase from each particle. The monopropellant flamelet diffuses into the reactive gas of the base matrix above the burning surface and a homogeneously mixed gas is formed. 

Since the energy contained within double-base propellants is limited because of the limited energies of nitrocellulose (NC) and nitroglycerin (NG), the addition of ammonium perchlorate or energetic nitramine particles such as HMX and RDX increases the combustion temperature and specific impulse. Extensive experimental studies have been carried out on the combustion characteristics of composite-modified double-base (CMDB) propellants containing AP, RDX or HMX parhclesli- l and several models have been proposed to describe the burning rates of these pro-... 

Kubota, N Energetics of HMX-Based Composite-Modified Double-Base Propellant Combustion, J. of Propulsion and Power, Vol. 15, No. 6,1999, pp. 759-752. 

Singh, H., Advances in Composite-Modified Double-Base Propellants (Eds. Varma, M., and Chatterjee, A. K.),... 

Another substantial increase in delivered energy was obtained by incorporating substantial amounts of solid oxidizer e.g., ammonium perchlorate) and metallic fuel e.g., aluminum) in the casting powder. The resulting family of composite-modified double-base (CMDB) propellants has found widespread use in ballistic missiles and space motors. 

The data reported in the literature suggests that the replacement of DEP by Bu-NENA in the Dense NC/NG+ DEP/AP/AI/RDX-based composite modified double-base (CMDB) propellants results in increase in the burn rate by 18-20% at 70 kg cm pressure. The calorimetric value and percentage elongation also increase significantly. Further, thermal stability and sensitivity of such propellants are comparable with DEP-based CMDB propellants [184]. Bu-NENA is also a component of low vulnerability ammunition (LOVA) propellants [185, 186]. The introduction of butyl-NENA into SB, DB and gun propellants results in improvement of their mechanical properties and energetics and reduction in their sensitivity [187]. 

The Armed Forces demand a long shelf-life (min 10-12 years) for propellants for use in different rockets and missiles. However, the shelf-life of propellants is limited. There are some chemicals which on their addition to these propellants during their manufacture retard the processes responsible for their deterioration and consequently, increase their shelf-life. The main purpose of addition of these chemicals in propellant formulations is to enhance their shelf-life without adversely affecting their manufacturing processes and properties. Such chemicals or additives are known as stabilizers in case of DB and composite modified double-base (CMDB) propellants whereas anti-oxidants in the case of composite propellants. The additives for this purpose are therefore selected depending on the type of propellant. 

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