Propellants homogeneity

Copredpitation Batch mode vs. continuous mode Flow rate Droplet size distribution Mixer design (shear and energy, e.g., stir bar, vortex, propeller, homogenizer, rotor-stator) Solvent to antisolvent ratio Temperature Processing times (scale dependent)... 

Solutions. To dehver a spray, the formulated aerosol product should be as homogeneous as possible. That is, the active ingredients, the solvent, and the propellant should form a solution. Because the widely used halocarbon and hydrocarbon propellants do not always have the desired solubiUty characteristics for all the components in the product concentrate, special formulating techniques using solvents such as alcohols (qv), acetone (qv), and glycols (qv), are employed. 

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. 

Pyrotechnic mixtures may also contain additional components that are added to modify the bum rate, enhance the pyrotechnic effect, or serve as a binder to maintain the homogeneity of the blended mixture and provide mechanical strength when the composition is pressed or consoHdated into a tube or other container. These additional components may also function as oxidizers or fuels in the composition, and it can be anticipated that the heat output, bum rate, and ignition sensitivity may all be affected by the addition of another component to a pyrotechnic composition. An example of an additional component is the use of a catalyst, such as iron oxide, to enhance the decomposition rate of ammonium perchlorate. Diatomaceous earth or coarse sawdust may be used to slow up the bum rate of a composition, or magnesium carbonate (an acid neutralizer) may be added to help stabilize mixtures that contain an acid-sensitive component such as potassium chlorate. Binders include such materials as dextrin (partially hydrolyzed starch), various gums, and assorted polymers such as poly(vinyl alcohol), epoxies, and polyesters. Polybutadiene mbber binders are widely used as fuels and binders in the soHd propellant industry. The production of colored flames is enhanced by the presence of chlorine atoms in the pyrotechnic flame, so chlorine donors such as poly(vinyl chloride) or chlorinated mbber are often added to color-producing compositions, where they also serve as fuels. 

Metallacarboranes. These are used in homogeneous catalysis (222), including hydrogenation, hydrosilylation, isomerization, hydrosilanolysis, phase transfer, bum rate modifiers in gun and rocket propellants, neutron capture therapy (254), medical imaging (255), processing of radioactive waste (192), analytical reagents, and as ceramic precursors. 

A solid propellant is a mechanical (heterogeneous) or a chemical (homogeneous, or colloidal) mixture of solid-state fuel and oxidizer-rich chemicals. Specially-formed charges of solid propellant (grains) arc placed in the combustion chamber of the solid rocket motor (SRM) at a production facility. Once assembled, the engine does not require additional maintenance, making it simple, reliable and easy to use. 

The vivid interest in hydrazine as a powerful propellant has stimulated many investigations both of its thermal decomposition and of its oxidation. Although hydrazine decomposes much more readily than ammonia, the study of its homogeneous decomposition by classical means using a static system is complicated considerably by wall catalysis. Thus, other experimental techniques have had to be applied, e.g. decomposition flames, flash photolysis, studies of explosion characteristics and the shock-tube technique. 

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. 

Sawyer, R. F., The Homogeneous Gas-Phase Kinetics of Reactions in Hydrazine-Nitrogen Tetraoxide Propellant System, Ph.D. Thesis, Princeton University, 1965. 

Lengelle, G., Bizot, A., Duterque, J., and Trubert, J. F., Steady-State Burning of Homogeneous Propellants, Fundamentals of Solid-Propellant Combustion (Eds. Kuo, K. K., and Summerfield, M.), Progress in Astronautics and Aeronautics, Vol. 90, Chapter 7, AlAA, New York (1984). 

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. 

HMX composite propellants are composed of crystalline HMX particles and polymeric materials, and so their physical structures are heterogeneous. On the other hand, nitropolymer propellants are composed of mixtures of nitrate esters such as NC and NG, and their physical structures are homogeneous. Moreover, HMX pro-... 

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... 

Qualitative. The propellant shall be a colorless, homogeneous liquid when examined visually by transmitted light... 

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)... 

After several days to 2 weeks at the elevated cure temperature, the propellant has been converted to a macroscopically homogeneous mass by mutual diffusion of nitrocellulose and plasticizers. The propellant charge is then permitted to cool to room temperature, casting fixtures are disassembled, cores are extracted, and finally the propellant end surfaces are machined to conform to required dimensions. 

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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