Solid propellant formulations

Chan, M. L, Reed, Jr., R., and Ciarami-taro, D. A., Advances in Solid Propellant Formulations, Solid Propellant Chemistry, Combustion, and Motor Interior Ballistics (Eds. Yang, V., Brill, T. B., and Ren, W.-Z.), Progress in Astronautics and Aeronautics, AlAA, Vol. 185, 2000, Chapter 1.7. 

A solid propell formulation based on HAP has been patented (Ref 2). It contains about 80%... 

The flexibility inherent in the polymer manufacturing procedure allowed for the synthesis of many variations of polymer. The examination of these materials in propellant formulations by scientists at the Jet Propulsion Laboratories, Thiokol Chemical Corp., and later other propellant companies not only resulted in many useful solid propellant formulations but laid a significant portion of the foundation on which the propellant chemists of today continue to build. 

Crosslinks can be controlled by the number of unsaturated sites in the polyester prepolymer. Theoretically if each molecule has only two reaction sites, then infinite, almost linear, chains could be obtained. Hence, average functionability and molecular weight distribution in the prepolymer are extremely important. Plasticizers can be used to advantage in adjusting the average properties of the binder as obtained in the solid propellant formulation. 

A hydrocarbon prepolymer containing terminal carboxyl groups (28) is available to the propellant chemist. These polymers were synthesized to eliminate some of the variables found in the copolymers. The carboxyl groups can be made of the same types with like reactivity. These linear non-branched polymers impart greater extensibility to elastomeric formulations. The chemistry in propellants is similar to the random functionality polymer. As 20 years of the chemistry of crosslinked propellant binders is reviewed, one familiar with the art cannot fail to predict solid propellant formulations using these polymers tailored to the specific requirements of the solid rocket design with the confidence that any discipline of science can be practiced. 

Compatability of ingredients is always important. Particularly important to safe handling is the autoignition temperature and friction sensitivity of the propellant. Small changes in the formulation can often effect these important properties. An example is the sensitivity of some propellant formulations to extremely small amounts of chlorate. Safety precautions must always include consideration of the chemistry. By following this practice, the propellant industry has experienced an excellent safety record while making unusual progress in the application of viscoelastic materials in case-bonded solid propellant rockets. 

Figure 9. Typical stress-strain curve for solid propellants at 0.77 in./min. and 80°F. E is the slope of the tangent to the initial portion of the curve. A variety of curve shapes are possible depending on specific formulations and test conditions...

In a recent attempt to bring an engineering approach to multiaxial failure in solid propellants, Siron and Duerr (92) tested two composite double-base formulations under nine distinct states of stress. The tests included triaxial poker chip, biaxial strip, uniaxial extension, shear, diametral compression, uniaxial compression, and pressurized uniaxial extension at several temperatures and strain rates. The data were reduced in terms of an empirically defined constraint parameter which ranged from —1.0 (hydrostatic compression) to +1.0 (hydrostatic tension). The parameter () is defined in terms of principal stresses and indicates the tensile or compressive nature of the stress field at any point in a structure —i.e.,... 

Many chemical and physical analysis techniques have been applied to the study of solid propellant aging. Valuable contributions have been made in improving formulations and in establishing confidence in the stability of propellants for a variety of applications. Fortunately, many... 

A family of high performance and clean space motor/gas generators and large launch vehicle solid propellants based on poly(GlyN) binder, ammonium nitrate oxidizer and small amounts of aluminum and/or boron with optimized performance at low solids loading (without the presence of plasticizers) and also poly(GlyN) binder, ammonium nitrate oxidizer and aluminum or magnesium fuel have been reported in the literature [141, 142]. These solid propellant formulations produce essentially no HC1 or chloride ions in the exhaust and are considered eco-friendly. 

Bum rates of propellants are inversely proportional to the particle diameter of Al powder particles. This is corroborated by the increase in bum rate of propellants on incorporation of Alex in their formulations. The bum rate of solid propellant increases by about 100% on replacement of 9% Al by Alex powder (in a total of 18% Al) coupled with decrease in pressure index. 

Similar to the effects of Alex addition in pyrotechnics and solid propellants, replacement of conventional micron-sized A1 powder by nanosized A1 powder (Alex) increases the detonation velocities and heats of detonation of TNT/A1 formulations. The increase of VOD is more pronounced in small diameter charges, close to the critical diameter. On the contrary, n-Al powder does not increase the VOD of aluminized PBXs based on inert binders. It is very interesting to observe that the VOD of PBXs based on an energetic binder decreases on substitution of micron-sized A1 by Alex [119, 120]. Reshetov and his coworkers [121] reported in the early 1980s that the addition of Alex enhanced VOD of RDX. More recently, an increase in both VOD as well as brisance was demonstrated for a number of TNT-based tritonal and H-6 formulations containing Alex. The improvements in VOD -200-300ms1 and brisance up to 27% were observed in a number of tritonal charges on replacement of conventional or micron-sized A1 by Alex [122]. 

Combustion of Zirconium Particles Used in Solid Propellant Formulations , Vd H, ibid, 221-244 25) J.D. Martin et al, High Density... 

J.Reinhart et al of NOL, "Nitrasol Propellants -Composite Propellant Formulations Based on a Plastisol-Nitrocellulose-Pentaerythritol Trinitrate Binder (U), Bull of the 14th Meeting of the Joint Army-Navy-Air Force Solid Propellant Group, Johns Hopkins University, Silver Spring, Md(1958)(Conf)(Not used as a source of info) 1)... 

Another non-equilibrium effect arises when the product composition contains a condensible substance. Solid propellant formulations based upon potassium perchlorate form solid potassium chloride and the acetylenic monopropellants upon decomposition form large quantities of carbon particles, as do very fuel-rich mixture ratios of hydrocarbon propellant systems. More recently metal and metal compounds have been used as fuels and form product oxides which are very high boiling point compounds that condense to varying degrees in the rocket chamber and nozzle. For example, estimates indicate that the normal boiling points of Li20, BeO,... 

In recent years, the great majority of solid rockets have utilized composite propellants. Most composite propellants are based on a solid oxidizer and a curable liquid polymeric binder. The binder also serves as fuel. Optionally, metallic fuels such as aluminum or boron may also be used.45 The propellant components are mixed together, and then the binder is cured to give the tough, flexible, elastomeric (rubbery thermoset) solid propellant required for modem missile use. An excellent source of information on the formulation of solid propellants is a report by Oberth.46... 

Binder. The binder of a composite solid propellant serves the dual function of providing a matrix to hold the oxidizer and the metal fuel, and of serving as a fuel itself—although its total makeup in modem formulations may only be 8-10 wt percent. The binder of the propellant usually is considered to consist of the polymer, the curing agent, and the plasticizer—and can arguably include soluble stabilizers, as well. 

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