AP-HTPB Propellants

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. 

Fig. 7.6 Burning rate versus (BDR) of oxidizer-rich AP-HTPB propellants at 3.5 MPa.

Fig. 7.7 Burning rate of an oxidizer-rich AP-HTPB propellant with the composition htpb(0 08) if low-pressure region.

Fig. 7.9 Heat flux and heat of reaction in the gas phase and in the condensed phase for an oxidizer-rich AP-HTPB propellant at low pressures below 0.1 M Pa.

Fig. 7.16 EfiFect of (HTPB) on the burning rate and adiabatic flame temperature of AP-HTPB propellants.

Fig. 12.21 shows the combustion products of AP-HTPB and RDX-HTPB composite propellants. Large amounts of H2O, HCl, and CO2 are formed when an AP-HTPB propellant composed of a.p(0.85) is burnt. The molecules of H2O, HCl, and CO2 each emit infrared radiation. On the other hand, no COj or C(g) is formed when an RDX-HTPB propellant composed of ri3x(0.85) is burnt. Instead, large amounts of CO, H2, and Nj molecules are formed as its major combustion products. However, no infrared radiation is emitted from H2 or N2 molecules. Though CO molecules are formed at ri3x(0.85), the infrared radiation emitted from these is less than that from H2O or CO2 molecules. 

Keizers, H.L.J. (1995) Accelerated ageing of AP/HTPB propellants and the influence of various environmental ageing conditions. Proc. Inti. Symp. on Energetic Materials Technology, American Defense Preparedness Association, Phoenix, Arizona, USA, Sept. 24-27, 1995, p. 199. 

The AP-HTPB propellant produces relatively high concentrations of solid carbon and hydrogen chloride (HC1). Though the mass fraction of the fuel components increases as the mass fraction of HTPB increases, the self-sustaining burning of AP-HTPB propellant becomes impossible because of the heat of decomposition becomes too low to maintain its thermal decomposition. On the other hand, the N C-NG propellant burns to generate fuel-rich products even when the mass fraction of NC increases. However, the mechanical properties of NC-NG propellant become poor. Furthermore, the burning rate of AP-HTPB and NC-NG propellants becomes low and the pressure exponent also becomes too low for their use as ducted rocket propellants. 

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