Ballistic modifiers

Polymer-based rocket propellants are generally referred to as composite propellants, and often identified by the elastomer used, eg, urethane propellants or carboxy- (CTPB) or hydroxy- (HTPB) terrninated polybutadiene propellants. The cross-linked polymers act as a viscoelastic matrix to provide mechanical strength, and as a fuel to react with the oxidizers present. Ammonium perchlorate and ammonium nitrate are the most common oxidizers used nitramines such as HMX or RDX may be added to react with the fuels and increase the impulse produced. Many other substances may be added including metallic fuels, plasticizers, stabilizers, catalysts, ballistic modifiers, and bonding agents. Typical components are Hsted in Table 1. 

Amorphous carbon comprises various combinations of carbon atoms. Charcoalis a typical amorphous form of carbon and is used as a major component of black powder and ballistic modifiers of rocket propellants. Charcoal contains a large number of tiny pores and the total surface area within the structure is approximately 1-3 m mg This surface area plays a significant role as a catalytic surface in various chemical reactions. It is well known that the burning rate of black powder is very fast because of the large surface area of the carbon structure. 

Gun and rocket propellants are based on nitrocellulose (NC-SB), NC with NG as second principal ingredient (DB) and nitroguanidine (picrite) in addition to NC and NG ( ) propellants. Propellant formulations also contain stabilizer, plasticizer, coolant and ballistic modifier, in addition to their principal ingredients. 

The binder should be compatible with the other ingredients of the propellant, that is, oxidizer, metal powder, plasticizer, bonding agent, stabilizer and ballistic modifier etc. 

In addition to fuel, oxidizer and inert/energetic plasticizer, various additives are also included in the propellant formulations in order to improve their mechanical or ballistic properties. One such additive is termed a burn-rate (ballistic) modifier which alters inherently high dependence of the burn rate on chamber pressure. The use of an additive for this purpose depends on the type of propellant, that is,... 

Short sections of thin metal wires (good conductor of heat) such as , Pb, Al, Cu, Ag and Mo Increase burn rates of DB propellants containing ballistic modifiers such as lead salts of salicylic and 2-ethylhexanoic add without any adverse effect on the plateau region [240]. 

Zinc oxide in conjunction with one or more conventional ballistic modifiers-lead stearate, lead acetophthalate, lead-P-resorcylale and basic copper salicylate etc. Propellants exhibit good quality plateau burning over a useful pressure range for a wide range of burn rates [241]. 

The simplest way to modify the bum rate of composite propellants is by means of catalysts or ballistic modifiers. The solid catalysts that have been in use for many years can be classified into two groups. 

Sayles, D.C. (1975) Propellant composition of NC-type containing non-lead ballistic modifiers. US Patent 3,860,462. 

Neidert, J.B., and Askins, R.E. (1994) Castable DB propellant containing ultrafine carbon fiber as a ballistic modifier. US Patent 5,372,664. 

Huskins, C.W., and Williams, L.J. (1983) Silane ballistic modifier containing propellant. US Patent 4,412,874. 

A premix is prepared by mixing the fuel binder (i.e. a polysulphide rubber in the case of the Thiokol propellant) with the necessary curing agents, inert additives, and ballistic modifiers in a double-acting paddle mixer. This mixer is equipped... 

The expl props of DATNB are given in Ref 8. DATNB is used as a pressed HE, and also used as a ballistic modifier in some rocket propints (Ref 11)... 

Propellants. Satriana and Bracuti (Ref 30) claim the use of pyrolyzed urea as a ballistic modifier which when incorporated in a doublebase plastisol propint produces a burning rate plateau. Thus, PbSnC>3 (90) and urea, acet and w (10g) are sintered for one hr at 500—50°, cooled, screened, molded and cured for use in a plastisol proplnt contg 30% HMX. Leach (Ref 37) reports that ballistic and other test results indicate that there is no significant difference between M30 proplnt contg Nitroguanidine prepd by the urea/AN process and that prepd by the standard British fusion process. 

Cobalt-Chromiun Acetoacetonate, CoCr-(CH3.CO.CH2COO)s( ). This compd is listed by Swotinsky without giving its formula, method of prepn, props or refs) as one of the ingredient s of experimental rocket propints, as a ballistic modifier to replace... 

TDI has a flash pt of 132° (open cup) and flammable vapor level limits of 05 to 9.5% 2,4-Tolylene diisocyanate is used as a constituent (cross-linking agent) of polyurethane expls, proplnt binders, and as a component of a ballistic modifier (Refs 2a, 8 9). Se in Vol 8, P6 8-Table 3 under PBX Type Explosives-Composition (listed as Polyurethane in the Binder, % column), and P409-R to P415-Table 17 under B. Composite Propellants ... 

Triple-base propellants have also been produced, having double-base composition plus nitroguanidine, added as a combustion coolant or as a ballistic modifier. 

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