Homogenization with propellers

A density difference significantly lengthens the mixing time  

In general one of two hydrodynamic conditions occur upon mixing with propellers  

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This result shows, that homogenization can be carried out exceptionally favorably with gas throughput. Compared with propeller stirrers, power values are obtained which are of the same order of magnitude, only the investment costs in the case of a gas sparger with compressor are incomparably lower. 

Single-base propellants are mixed in a similar fashion by adding the ingredients to the nitrocellulose in the mixer together with the required amounts of ether and alcohol. The mixing time is about one-half hour, and the temperature is kept below 25°C. The pardy colloidal mixture looks like moist cmde sugar. A maceration step may be included to increase homogeneity. 

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... 

The influence of temperature on detonability limits was not determined in the laboratory of Dr Price, but only search of literature is repotted. There are few data showing a limit curve in the diameter-temperature plane, but one set for NMe (Nitromethane) was reported by Campbell et al (Ref 4a) to exhibit the expected decrease in critical diameter with increase in temperature. However, NMe is a physically homogeneous liquid expl and its behavior differs, probably, from that of heterogeneous expls. Of the two references mentioned by Price, one (Ref 15) concerns granular charges of AN, while the other (Ref 16) deals with one propellant compn. In both cases, there seems to be a marked lowering of... 

CA 74, 14697(1971) (Propellant contg GuPchl-LiPchl eutectics in homogeneous phase with polymeric binders) (GuPchl/LiPchl, mp 70/30, 126.5° 66.8/33.2, 151° 57.5/42.5, 110°. These are much less sensitive to impact than LiPchl alone. The polymerization of the binder should not produce w, eg, acrylamide is acceptable)... 

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. 

From a practical standpoint, a system is considered cured when mechanical and ballistic properties show no further change with storage at cure temperature. However, propellant that is fully cured does not exhibit a perfectly homogeneous distribution of ingredients. 

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