Leaded double-base propellant

Most composite propellants in wide use today use ammonium perchlorate as the oxidizer component. While such propellants benefit from high specific impulse and a lower vulnerability than double-base propellants based on nitroglycerine, they have a significant environmental impact, the exhaust fumes being rich in corrosive hydrogen chloride leading to acid rain after the launch of missiles/rockets. 

When nitramine particles such as HMX or RDX particles are mixed with a doublebase propellant, nitramine composite-modified double-base propellants are formulated. Since HMX and RDX are stoichiometrically balanced materials, the use of these nitramine particles leads to a somewhat different mode of combustion as compared to AP-CMDB propellants. Since each nitramine particle can burn independently of the base matrix at the burning surface, a monopropellant flamelet is formed in the gas phase from each particle. The monopropellant flamelet diffuses into the reactive gas of the base matrix above the burning surface and a homogeneously mixed gas is formed. 

Steinberger and Carderl24.25] measured the burning rates of liquid strands composed of 63 % nitroglycerin and 37 % diethylene glycol. When 5 % lead aspirate was added to the basic liquid strand, they observed an increased burning rate between 4.0 MPa and 13.5 MPa. This effect is qualitatively the same as in the case of a double-base propellant. The burning rate of the liquid strand was increased by 70 % at 6.8 MPa by the addition of the lead aspirate. 

Fig. 6.23 Burning rates of catalyzed NC-NG and NC-TMETN double-base propellants, showing two platonized regions for both propellants resulting from the addition of a combination of two lead compounds.

Fig. 6.25 Increased burning rates of a double-base propellant resulting from the addition of metallic copper and/or lead powders.

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-... 

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. 13.16 Stable, oscillatory, and unstable burning zones for a lead-catalyzed double-base propellant.

Obviously, typical composite propellants are highly filled polymers and, especially in the case of the rubber-based systems, are more nearly granular media than merely filled rubbers. Certain specific differences between the double-base binder and the elastomeric binder lead to some differences in behavior, but many of the resulting properties show similarities. The relationships between bulk properties and microstructure in the rubber-based systems are much better understood than those of the double-base propellants and, therefore, the following discussions focus primarily on the former category. 

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. 

Addnl Refs (Limited Distribution) A) A.T. Camp, Research, Development and Large-Scale Application of Temperature-Independent Double-Base Propellants A Brief Survey and History , IHSP 68-14 (1968) B) R.M. Abbott N.S. Gelber, Analysis of Lead and Copper Salts of Hydroxy-Substituted Benzoic Acids , PATR 4376 (1972)... 

Lead acetylsalicylate is a combustion-modifying additive, especially so in rocket propellants based on double base powder -> Double Base Propellants. 

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. 

---