Burning Rates and Thermal Behavior of Bistetrazole Containing Gun Propellants

Abstract

The influence of two selected bistetrazoles, 5,5′‐bis(1H‐tetrazolyl)‐amine (BTA) and 5,5′‐hydrazinebistetrazole (HBT), on the combustion behavior of a typical triple‐base propellant was investigated. Seven propellant formulations, one reference and six others incorporating 5 %, 15 %, and 25 % of either HBT or BTA compounds, respectively, were mixed and extruded into a cylindrical, no perforations, geometry. The resulting propellants showed high burning rates, up to 93 % higher than the reference formulation at 100 MPa. However, the increase in burning rates came at the cost of higher burning rate dependency on pressure, with a pressure exponent as high as 1.4 for certain formulations. HBT‐containing propellants showed notably lower flame temperature when compared to the reference formulation, with a flame temperature reduction of up to 461 K for the propellant containing 25 % HBT. The thermal behavior of the propellants was also investigated through DSC experiments. The addition of bistetrazoles provided lower decomposition temperatures than the pure nitrogen‐rich materials, indicating that the two compounds probably react readily with the −ONO2 groups present in the nitrocellulose and the plasticizers used in the formulation. The onset temperature of all propellants remained within acceptable ranges despite the observed decrease caused by the addition of the bistetrazole compounds.

Erosivity and Performance of Nitrogen‐Rich Propellants

“…In addition to the increased burning rates, there is also a significant change in the linear burn rate coefficients and pressure exponents. This is different from the previously re-ported burning rate law parameters for propellants containing BTA and HBT where an increase in pressure exponent was observed rather than a decrease [14]. This agrees with the statement that mixtures of nitrogen-rich materials with other energetics can show an increase in pressure exponent and a decrease in linear burn rate coefficient followed by the reverse when the nitrogen-rich content increases.…”

“…It goes without saying that new propellants designed to have lower erosivity should also provide equal or better performance than the propellants they are designed to replace. The positive effects of nitrogen-rich materials on the burning rate of propellants have already been demonstrated by Mason et al and Lavoie et al [13,14]. It was shown that in certain cases, despite the lower flame temperature, the experimental maximum pressure observed for nitrogen-rich propellants in a closed vessel was equivalent to that of formulations that did not incorporate nitrogen-rich materials, an indication that the same performance level is attainable [14].…”

“…Five propellants were used in this work: a standard simple base propellant (SB), a modified JA2 triple-base propellant (designated JAM), the same reference triple-base used in a previous work (MTB17) [14] and two propellants each incorporating one nitrogen-rich crystal at 35 % weight concentration, either BTA (MTB16) or HBT (MTB15). Table 7 shows the composition of the propellants.…”

“…SB was also provided by GD-OTS Valleyfield. Finally, the two propellants incorporating nitrogen-rich materials were manufactured using the facilities available at DRDC-Valcartier in a 1 USG (3.7 L) Bayer-Perkins sigma blade mixer, as described previously [13,14]. All propellants were extruded to a cylindrical 7 perforations geometry.…”

“…It was shown that in certain cases, despite the lower flame temperature, the experimental maximum pressure observed for nitrogen-rich propellants in a closed vessel was equivalent to that of formulations that did not incorporate nitrogen-rich materials, an indication that the same performance level is attainable [14]. This work is a follow up on the previous one [14] and focuses on the effects of two nitrogen-rich materials on the erosivity of gun propellants comparatively to standard formulations with matching impetus.…”