Propellants catalyzed

Fig. 6.22 shows a typical set of burning rates for catalyzed and non-catalyzed NC-NG double-base propellants. The burning rate of the non-catalyzed propellant composed of 53 % NC, 40% NG, and 7 % DEP is seen to increase linearly with increasing pres sure in an In r versus In p plot. When the propellant is catalyzed with a com-... 

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.

Table 6.9 Chemical compositions of non-catalyzed and catalyzed propellants % by mass).

Though it is impossible to formulate a complete mathematical representation of the super-rate burning, it is possible to introduce a simplified description based on a dual-pathway representation of the effects of a shift in stoichiometry. Generalized chemical pathways for both non-catalyzed and catalyzed propellants are shown in Fig. 6.26. The shift toward the stoichiometric ratio causes a substantial increase in the reaction rate in the fizz zone and increases the dark zone temperature, a consequence of which is that the heat flux transferred back from the gas phase to the burning surface increases. 

The dark zone length of liF-catalyzed propellants is increased by the addition of LiF in the region of super-rate burning, similar to the case of Pb-catalyzed propellants, as shown in Fig. 6.28. Table 6-11 shows the dark zone lengths and reaction times Xg in the dark zone producing the luminous flame at two different pressures,... 

Fig. 6.29 shows the effect, or lack thereof, of the addihon of Ni particles on the burning rate of a double-base propellant. The double-base propellant is composed of Nc(0-44), ng(0.43), i3gp(0.11), and Iec(0-02) as a reference propellant. This propellant is catalyzed with 1.0% Ni particles (2 pm in diameter). No burning rate change is seen upon the addition of Ni particles.F However, the flame structure is altered significantly by the addition of Ni. The flame stand-off distance between the burning surface and the luminous flame front is shortened, as shown in Fig. 6.30. Though the flame stand-off distance of the reference propellant is about 8 mm at 1.5 MPa and decreases rapidly with increasing pressure (1 mm at 4.0 MPa), the flame stand-off distance of the Ni-catalyzed propellant remains unchanged (0.3 mm) when the pressure is increased.

Fig. 7.45 shows a set of flame photographs of HMX-GAP propellants with and without catalysts. The luminous flame front of the non-catalyzed propellant is almost attached the burning surface at 0.5 MPa (a). When the propellant is catalyzed, the luminous flame is distended from the burning surface at the same pressure (b). Since the heat flux transferred back from the gas phase and the heat of reaction at... 

The combustion wave structure of HMX propellants catalyzed with LiF and C is similar to that of catalyzed nitropolymer propellants the luminous flame stands some distance above the burning surface at low pressures and approaches the burning surface with increasing pressure. The flame stand-off distance from the burning surface to the luminous flame front is increased at constant pressure when the propellant is catalyzed. The flame stand-off distance decreases with increasing pressure for both non-catalyzed and catalyzed propellants. 

Like double-base propellants, CMDB propellants show super-rate and plateau burning when they are catalyzed with small amounts of lead compounds. Fig. 8.21 shows a typical plateau burning for a propellant composed of NC-NG and HMX.P I The chemical composition of the catalyzed propellant is shown in Table 8.1. 

Fig. 8.22 The luminous flame front of the platonized propellant approaches the burning surface more rapidly than that of the non-catalyzed propellant when the pressure is increased in the plateau-burning pressure region.

Fig. 8. 23 Temperature gradient in the fizz zone increases in the super-rate burning region and then remains unchanged in the plateau-burning pressure region for the catalyzed propellant.

Fig. 8.24 Catalyst activity in the fizz zone decreases rapidly in the plateau region and becomes negative above the pressure region in which the burning rate of the catalyzed propellant is lower than that of the non-catalyzed propellant.

Since cjijand r of the catalyzed propellant are pressure-independent in the plateau region and Qf is nearly constant, oiy should also be pressure-independent. This is a significant difference when compared with commonly observed bimolecular gas-phase reactions. Referring to Eq. (3.33), the reaction rate in the gas phase, oig, is given as a function of pressure according to... 

The effective overall order of the fizz zone reaction, k, is determined to be zero for plateau burning, and approximately 1.4for super-rate burning. The reaction order for the non-catalyzed propellant is also determined to be approximately 1.7, that is, nearly equal to the order of a conventional gas-phase reaction. 

Fig. 13.15 Pressure versus time curves for a lead-catalyzed propellant in a rocket motor. 

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