Burning-rate catalysts, double-base

A Comparison of Crosslinkable Double-Base Propellants With and Without Burning Rate Catalyst... 

There are plateau propellants that exhibit an intermediate range of pressure over which m is practically independent of p and mesa propellants for which m(p) achieves a maximum at a particular value of p then a minimum at a higher value. These effects may be produced in conventional double-base propellants by suitable addition of burning-rate catalysts (typically certain metal-organic salts) to the propellant formulation. It has been shown experimentally that these catalysts usually operate by modifying the interaction between the condensed-phase and dispersed-phase reaction zones [57], [58]. Thus dispersion phenomena are of importance to the deflagration of homogeneous propellants in a number of ways. 

Experimental results indicate that various phenomena occur on platonized propellants.When lead catalysts are added to high-energy double-base propellants, no super-rate burning occurs. Lead catalysts only act effectively on low-energy double-base propellants. On the other hand, lead catalysts are known to retard the rate of aldehyde oxidation. Carbonaceous materials are formed on the burning sur-... 

Combustion tests carried out for a rocket motor demonstrate a typical T combustion instability. Double-base propellants composed of NC-NG propellants with and without a catalyst (1 % nickel powder) were burned. Detailed chemical compositions of both propellants are given in Section 6.4.6 and the burning rate characteristics are shown in Fig. 6.29. The addition of nickel is seen to have no effect on burning rate and the pressure exponent is n = 0.70 for both propellants. 

The effects of the catalyst on burning rate and flame reaction indicate that the super-rate burning phenomena observed in the combustion of HMX-CMDB propellants are fundamentally the same as the combustion phenomena of catalyzed double-base propellants. This implies that the lead catalysts act on the combustion of HMX to produce super-rate burning. 

Low-frequency oscillation in a rocket motor depends on the pressure exponent of propellant burning rate and the free volume of the chamber. [ -7] when a double-base propellant composed of nc(0 510), ng( - 55), and dep(0.120), with pbsa(0.015) as a platonizing catalyst, bums in a strand burner, the burning rate characteristicsmay be divided into four zones, as shown in Fig. 13.14. The pressure exponent varies between the pressure zones n = 0.44 in zone I above 3.7 MPa, n= 1.1 in zone II between 3.7 MPa and 2.1 MPa, n = 0.77 in zone III between 2.1 MPa and 1.1 MPa, and n = 1.4 in zone IV below 1.1 MPa. 

As described in Section 6.4, lead catalysts act on the condensed phase and fizz zone reactions, not on the dark zone reaction, and increase the burning rate. On the contrary, Ni catalysts act on the dark zone reaction, but not on the condensed phase or fizz zone reactions, and do not increase the burning rate. No luminous flame is produced when double-base propellants burn, for example, at 0.5 MPa. However, when catalyzed propellants with metallic Ni or organic Ni compounds burn, a luminous flame is produced just above the burning surface at the same pressure. 

Figure 8. Concentration of lead on the surface of double-base rocket propellant extinguished from burning at different pressures. The burning rate shows a drop with the sudden decrease of the lead catalyst.

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