TMETN

Nitrate esters are characterized by -O-NO2 bonds in their structures. Typical nitrate esters used in propellants and explosives are nitrocellulose (NC), nitroglyc-erin(NG), triethyleneglycol dinitrate (TEGDN), trimethylolethane trinitrate (TMETN), diethyleneglycol dinitrate (DEGDN), and nitratomethyl methyl oxetane (NIMO). These nitrate esters are aU liquid at room temperature, with the excephon... 

Since NG is highly shock-sensitive, other types of nitrate esters can be used to formulate non-NG double-base propellants. DEGDN, TEGDN, and TMETN are typical examples of energetic nitrate esters that can be mixed with NC. These nitrate esters are less energetic than NG, and their sensitivities to friction and mechanical shock are accordingly lower than those of NG. Thus, the mass fraction of desensitizer used in propellant formulation can be lower than when NG is involved. The physicochemical properties of these nitrate esters are shown in Tabs. 2.3 and 2.5-2.7. 

TMETN is a liquid at room temperature and the production process of NG-TMETN propellants is the same as that described for NG-NG propellants. The shock sensitivity of TM ETN is sufficiently lower than that of NG that no desensitizers are needed for NC-TMETN propellants. Instead of the DEP or TA used as low energy density plasticizers and stabilizers of NC-NG propellants, TMETN is mixed with TEGDN, which is a dinitrate ester and hence a relatively high energy density material. Thus, the overall energy density of double-base propellants composed of NC-TMETN is equivalent to or even higher than that of NC-NG double-base propellants. 

The chemical compositions and thermochemical properties of representative NC-NG and NC-TMETN double-base propellants are compared in Table 4.9. Though the NC/NG mass ratio of 0.80 is much smaller than the NC/TMETM mass ratio of 1.38, the combustion performance in terms of Tf and Mg is seen to be similar, and 0 is 109 kmol K kg for both propellants. In the case of rocket motor operation, Igp and pj, are also approximately equivalent for both propellants. 

Table 4.9 Chemical compositions and thermochemical properties of NC-NG and NC-TMETN double-base propellants (10 MPa).

Though the major components of double-base propellants are NG-NG or NG-TMETN, various additives such as plasticizers, burning rate modifiers, or combustion instability suppressants are needed. Table 4.11 shows the materials used to formulate double-base propellants. 

Since the energetics of nitropolymer propellants composed of NC-NG or NC-TMETN are limited due to the limited concentration of oxidizer fragments, some crystalline particles are mixed within these propellants in order to increase the thermodynamic energy or specific impulse. The resulting class of propellants is termed composite-modified double-base (CMDB) propellants . The physicochemical properhes of CMDB propellants are intermediate between those of composite and double-base propellants, and these systems are widely used because of their great potential to produce a high specific impulse and their flexibility of burning rate. 

When crystalline AP particles are mixed with nitropolymers, ammonium perchlorate composite-modified double-base (AP-CMDB) propellants are formulated. A nitropolymer such as NC-NG or NC-TMETN double-base propellant acts as a... 

Fig. 6.18 shows a typical comparative example of the burning rates of two propellants composed of NC-TMETN and NC-NG. The chemical compositions (% by mass) and thermochemical properhes are shown in Table 6.5. The energy densities of these two propellants are approximately equivalent. 

Fig. 6.18 Burning rates of NC-NG and NC-TMETN doublebase propellants as a function of pressure.

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 6.8 Chemical compositions of catalyzed NC-TMETN and NC-NG double-base propellants (% by mass).

NG and NC-TMETN are not quite the same due to small differences in chemical structure and in the energy levels of the propellants, the burning characteristics of NC-NG and NC-TMETN propellants are broadly similar and the action of the catalysts in terms of producing super-rate, plateau, and mesa burning is the same for both propellants. 

Propellant NC Basic composition TMETN TECDN EC c Additives PbSa CuSa ... 

Super-rate burning occurs when lithium fluoride (LiF) is incorporated into NC-NG or NC-TMETN double-base propellants. As shown in Fig. 6.27, the burning rate of a propellant catalyzed with 2.4% LiF and 0.1% C increases drastically in the pressure region between 0.3 MPa and 0.5 MPa. This super-rate burning effect diminishes gradually as the pressure is increased above 0.5 MPa. The non-cata-lyzed propellant is a conventional NC-NG double-base propellant composed of 55 % NC, 35% NG, and 10% DEP. The maximum burning rate increase is about 230% at 0.5 MPa. 

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