Homogeneous double-base propellants

When an HMX-CMDB propellant burns steadily, the temperature in the condensed phase increases exponentially from the initial temperature T0 to the burning surface temperature Ts, as shown in Fig. 6-3. A rapid temperature rise occurs above the burning surface and reaches the temperature in the dark zone Tcj. The temperature is relatively constant up to a certain distance from the burning surface and increases again further downstream in the gas phase. The thermal structure of HMX-CMDB propellants appears to be similar to that of homogeneous double-base propellants even though HMX-CMDB propellants are heterogeneous. 

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. 

The combustion wave structure of RDX composite propellants is homogeneous and the temperature in the solid phase and in the gas phase increases relatively smoothly as compared with AP composite propellants. The temperature increases rapidly on and just above the burning surface (in the dark zone near the burning surface) and so the temperature gradient at the burning surface is high. The temperature in the dark zone increases slowly. However, the temperature increases rapidly once more at the luminous flame front. The combustion wave structure of RDX and HMX composite propellants composed of nitramines and hydrocarbon polymers is thus very similar to that of double-base propellants composed of nitrate esters.[1 1... 

Though the physicochemical properties of HTPE and HTPS are different, both are subject to a similar super-rate burning effect. However, the magnitude of the effect is dependent on the type of binder used. As in the case of double-base propellants, the combustion wave structures of the respective propellants are homogeneous, even though the propellant structures are heterogeneous and the luminous flames are produced above the burning surfaces. 

Curing. The curing process of a double-base propellant converts a bed of casting powder granules whose interstices are filled with casting solvent to a macroscopically homogeneous mass of propellant. It is convenient to discuss the theory of curing on a microscale and on a macroscale separately. 

Nitramine (RDX or HMX) oxidizer Homogeneous colloidal propellant consisting of nitrocellulose dissolved in plasticizer comprised of nitroglycerine and inert materials Composite or double-base propellant in which polymer is dissolved in plasticizier... 

There are plateau propellants that exhibit an intermediate range of pressure over which m is practically independent of p and mesa propellants for which m(p) achieves a maximum at a particular value of p then a minimum at a higher value. These effects may be produced in conventional double-base propellants by suitable addition of burning-rate catalysts (typically certain metal-organic salts) to the propellant formulation. It has been shown experimentally that these catalysts usually operate by modifying the interaction between the condensed-phase and dispersed-phase reaction zones [57], [58]. Thus dispersion phenomena are of importance to the deflagration of homogeneous propellants in a number of ways. 

Nitroglycerin is used to formulate explosives and is mixed with nitrocellulose as with double-base propellants. However, the mass fraction of NC is 0.06 - 0.08 for explosives and 0.3 - 0.6 for double-base propellants. Though both materials are homogeneous in their physical structures, the energy density of explosives is higher than that of double-base propellants because of the high mass fractions of NG. 

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