Catalyzed Nitramine Composite Propellants

Lead compounds are effective in increasing the burning rate (super-rate burning) of double-base propellants. A similar super-rate burning effect is observed when lead compounds are added to composite propellants consisting of nitramine particles and polymeric binder. Though the chemical structures and properties of nitramines are different from those of nitrate esters, super-rate burning effects are obtained by the use of the same lead compounds. 

The super-rate burning rates of HMX-HTPE and HMX-HTPS propellants are shown in Figs. 7-23 and 7-24, respectively. The basic chemical compositions and physicochemical properties of the noncatalyzed HMX-HTPE and HMX-HTPS propellants are the HMX-HTPE and HMX-HTPS propellants shown in Fig. 7-16, respectively. The catalysts, 2.4% PbSt and 0.4% carbon, are mixed with each noncatalyzed 

Though the physicochemical properties of HTPE and HTPS are different, the super-rate burning effects appear to be similar. However, the degree of the effect is dependent on the type of binder used. As with double-base propellants, the combustion wave structure of both propellants are homogeneous even though the propellant structures are heterogeneous and the luminous flames are produced above the burning surfaces. 

A typical super-rate burning of an HMX-GAP composite propellant is shown in Fig. 7-26. The lead catalyst is a mixture of lead citrate (LC PbCi), Pb3(C6Hs07)2-xH20, and carbon black (CB). The catalyzed HMX-GAP propellant consists of 19.4% GAP, 78% HMX, 2.0% LC, and 0.6% CB. GAP cured with 12.0% hexamethylene diisocyanate (HMDI) and crosslinked with 3.2% trimethylolpropane (TMP) is used to formulate GAP binder. The HMX particles are finely divided crystallized (3 HMX of bimodal particle size distribution (70% of 2 pm and 30 % of 20 pm in diameter). 

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In order to avoid the use of lead compounds on environmental grounds, lithium fluoride (liF) has been chosen to obtain super-rate burning of nitramine composite propellants.P7281 Typical chemical compositions of HMX composite propellants-with and without liF are shown in Table 7.4. The non-catalyzed HMX propellant is used as a reference pyrolant to evaluate the effect of super-rate burning. The HMX particles are of finely divided, crystalline (3-HMX with a bimodal size distribution. Hydroxy-terminated polyether (HTPE) is used as a binder, the OH groups of which are cured with isophorone diisocyanate. The chemical properties of the HTPE binder are summarized in Table 7.5. 

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