Density composite propellants

Oxidizers. The characteristics of the oxidizer affect the baUistic and mechanical properties of a composite propellant as well as the processibihty. Oxidizers are selected to provide the best combination of available oxygen, high density, low heat of formation, and maximum gas volume in reaction with binders. Increases in oxidizer content increase the density, the adiabatic flame temperature, and the specific impulse of a propellant up to a maximum. The most commonly used inorganic oxidizer in both composite and nitroceUulose-based rocket propellant is ammonium perchlorate. The primary combustion products of an ammonium perchlorate propellant and a polymeric binder containing C, H, and O are CO2, H2, O2, and HCl. Ammonium nitrate has been used in slow burning propellants, and where a smokeless exhaust is requited. Nitramines such as RDX and HMX have also been used where maximum energy is essential. 

Nitroguanidine (NQ) is a nitramine compound containing one N-NOj group in its molecular structure. In contrast to cyclic nitramines such as HMX and RDX, its density is low and its heat of explosion is also comparatively low. However, the Mg of its combustion products is low because of the high mass fraction of hydrogen contained within the molecule. Incorporating NQ particles into a double-base propellant forms a composite propellant termed a triple-base propellant, as used in guns. 

Azide polymers such as GAP and BAMO are also used to formulate AP composite propellants in order to give improved specific impulses compared with those of the above-mentioned AP-HTPB propellants. Since azide polymers are energetic materials that burn by themselves, the use of azide polymers as binders of AP particles, with or without aluminum particles, increases the specific impulse compared to those of AP-HTPB propellants. As shown in Fig. 4.15, the maximum of 260 s is obtained at (AP) = 0.80 and is approximately 12 % higher than that of an AP-HTPB propellant because the maximum loading density of AP particles is obtained at about (AP) = 0.86 in the formulation of AP composite propellants. Since the molecular mass of the combustion products. Mg, remains relatively unchanged in the region above (AP) = 0.8, decreases rapidly as (AP) increases. 

The ageing and low temperature properties of LTPB-based propellants have been reported to be comparable to the conventional CTPB-based propellants. Composite propellants possess higher densities (1.75-1.81 gem-3), higher specific impulse and a wide range of burn rates (7-20mms 1). Such propellants are generally made by the casting technique . Extruded composite propellants are also currently available. 

The copolymer of vinyl ferrocene (VF) and butadiene has also been reported in the literature for use as a binder for composite propellants. It does not require any burn-rate (BR) accelerator because of the presence of iron (Fe) in vinyl ferrocene which is converted to finely divided Fe203 (a well-known BR accelerator) during combustion. A few groups of scientists have also studied fluorocarbon polymers as binders for composite propellants because of their excellent compatibility with oxidizers and fuels coupled with high density. Accordingly, Kel-F elastomer (a copolymer of vinylidene fluoride and chlorotrifluoroethylene, trade name of 3M, USA) and Viton-A (copolymer of hexafluoropropylene and vinylidene fluoride, trade name of Du Pont, USA) have also been reported for this purpose. The structures of Kel-F 800 [Structure (4.13)] and Viton-A [Structure (4.14)] are ... 

As mentioned in Vol. 111. composite propellant detonate with difficulty because of their non-porous texture and very high density. 

The era of boron chemistry aimed at advanced jet and rocket propulsion systems ended in the early 1960s, however, the interest in the polyhedral boron hydrides as high energy density materials still persists and some salts of the c/o5o-decaborate and the c/oso-dodecaborate anions were proposed as components of components of high burning composite propellants [74]. However, the main interest in application of the polyhedral boron hydrides is connected with medicine [57,75] and traditionally centered on their use in boron neutron capture therapy for cancer [76,77]. 

Propellants cast into rockets are commonly case-bonded to the motors to achieve maximum volumetric loading density. The interior of the motor is thoroughly cleaned, coated using an insulating material, and then lined with a composition to which the propellant binder adheres under the environmental stresses of the system. The insulation material is generally a mbber-type composition, filled with siUca, titanium dioxide, or potassium titanate. SiUca-filled nitrate mbber and vulcanizable ethylene—propylene mbber have been used. The liner generally consists of the same base polymer as is used in the propellant. It is usually appHed in a thin layer, and may be partially or fully cured before the propellant is poured into the rocket. 

Fig. 6.18 shows a typical comparative example of the burning rates of two propellants composed of NC-TMETN and NC-NG. The chemical compositions (% by mass) and thermochemical properhes are shown in Table 6.5. The energy densities of these two propellants are approximately equivalent. 

Fig. 6.23 shows a comparison of the burning rates of catalyzed NC-NG and NC-TMETN propellants. As shown in Table 6.8, the chemical compositions of both propellants contain equal quantities of the same catalysts. The burning rates of the non-catalyzed NC-NG and NC-TMETN propellants are shown in Fig. 6.18. The energy densities of the two catalyzed propellants are approximately equal.

The physicochemical properties of propellants with the compositions hmx(0-4), Ihmx(0-6), and hmx(0-8) are shown in Table 7.3. Since the energy density of HMX is higher than that of GAP, the adiabatic flame temperatures of HMX-GAP propellants increase with increasing hmx-... 

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