Burning rate of artificially aged solid double-base gun propellants

Nitrocellulose (NC) and nitroglycerin (NG) are conventional energetic ingredients of solid double-base gun propellants. NC and NG are aliphatic nitrate ester compounds that are manufactured by nitrating through immersion in acid. Solid propellants are used in a wide range of both civilian and military applications, for example, as gas generators in airbags, as fuels in rocket motors or to shoot projectiles in guns. In all illustrations, the function of solid propellant is to generate gas, which is then employed to do mechanical work. The maximum pressure and the projectile velocity are important parameters of the interior ballistic process. The goal of the interior ballistic design of the gun is to attain a higher muzzle velocity under the smaller maximum chamber pressure. The burning rate of the propellant directly affects the formation rate of burning gases, which affects the ballistic parameters, either by diminishing the ballistic effectiveness or raising the safety hazard to the operator during firing. Note that the effect of the change of burning rate is not always negative; the fact is that we could change/control the burning rate to get better ballistic performances, includin ballistic efficiency as well as launching safety. Nevertheless, nitrate ester propellants are subjected to physical and chemical degradation during storage and this can modify the burning rate. Here we describe the effect of aging on the burning rate of spherical double-base propellants both qualitatively and quantitatively. We experimented unaged propellant, and propellant that was artificially aged at 71°C and 80ºC. The durations of heating at 71ºC were 10, 20, 30, 37, 48 and 62.5 days, respectively. The durations of heating at 80ºC were 1.8, 3.63, 5.41, 7.22, 9.02 and 10.83 days, respectively. The burning rate of investigating propellant was obtained by using closed-vessel experiments. The results show that towards low pressures, the burning rate increased with aging. Towards high pressure, the burning rate decreased as a function of aging. The effect of aging was quantified by the determination of defined aging sensitivity coefficients.