AN-GAP Composite Propellants

Fig. 4.16 Specific impulse, adiabatic flame temperature, and molecular mass of the combustion products for AN-GAP composite propellants.

When AN particles are mixed with GAP, AN-GAP composite propellants are formulated. The specific impulse is increased by approximately 10 s by replacing PB or PU binder with GAP, as shown in Fig. 4.16. The burning rate is also increased due to the exothermic decomposition of GAP. Since GAP burns by itself, the burning of the AN particles is supported by the exothermic decomposition reaction of the GAP at the burning surface of the propellant. As shown in Fig. 7.61, the burning rate is drastically decreased by the addition of AN particles. When is in-... 

Fig. 7.62 Relationship between adiabatic flame temperature and burning rate for AN-GAP composite propellants, showing that the burning rate decreases even though the flame temperature is increased by the addition of AN particles.

Hydrazinium nitroformate (HNF) contains a relatively high concentration of oxidizer fragments, as shown in Table 2.6. When GAP is used as a binder of HNF particles, HNF-GAP composite propellants are made. The maximum of 285 s and the maximum Tf of 3280 K are obtained at (HNF) = 0.90 with an optimum expansion from 10 MPa to 0.1 MPa, as shown in Figs. 4.20 and 4.21, respectively. Since a... 

A typical super-rate burning of an HMX-GAP composite propellant is shown in Fig. 7.43. The lead catalyst is a mixture of lead citrate (LC PbCi), Pb3(C5H50y)2-x H20, and carbon black (CB). The composition of the catalyzed HMX-GAP propellant in terms of mass fractions is as follows gap(0.194), hmx(0-780), lg(0 020), and, q 0.00G). GAP is cured with 12.0% hexamethylene diisocyanate (HMDI) and then crossUnked with 3.2 % trimethylolpropane (TMP) to... 

When these oxidizer particles are mixed with a binder such as HTPB, a nitropoly-mer, or GAP, the burning rate decreases with increasing mass fraction of ADN or HNF particles.[3+l Though the temperature sensitivity of an ADN composite propellant is significantly high in the low-pressure region, 0.005 at 1 MPa, it decreases... 

When HNF or ADN particles are mixed with a GAP copolymer with aluminum particles, an HNF-GAP or ADN-GAP composite propellant is formed, respectively. A higher specific impulse is obtained theoretically than the specific impulse of aluminized AP-HTPB composite propellants 37. However, the ballistic properties of ADN, CL-20, and HNF composite propellants such as pressure exponent, temperature sensitivity, combustion instability, and mechanical properties are needed to be improved drastically. 

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 polymeric binders used for nitramine composite propellants are similar to those used for AP composite propellants, i. e. HTPB, HTPE, and GAP. The combustion performance and the products of HMX composite propellants are shown in Figs. 4.17 and 4.18, respectively. Here, the binder mixed with the HMX particles is GAP, as in the AN-GAP propellants shown in Fig. 4.16. Though the maximum Tf and f, are obtained at (HMX) = 1.0, the maximum HMX loading is less than 0.80for practical HMX-GAP propellants, at which fp = 250 s and 7 =... 

The relative shock sensitivities of explosive compositions are commonly assessed by means of gap tests. In these tests, the shock from a standard donor explosive is transmitted to the test explosive through an inert barrier (the so called gap ). The shock sensitivity of the test explosive is characterized by the gap thickness for which the probability of detonation is 50%. In reference 26, the Los Alamos standard gap test and the Naval Ordnance Laboratory (NOL) large scale gap test were modeled using the 2DE code with Forest Fire burn rates. The Los Alamos gap test uses Dural for the inert barrier while the NOL gap test uses Plexiglas. The test explosive is unconflned in the Los Alamos gap test. In the NOL gap test the test explosive is confined with steel. The model showed good agreement between the calculated and experimental gap test values for PBX-9404, PBX-9502, Pentolite, Composition B, and an HMX based propellant, VTQ-2. 

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