Dissertation

Performance, Stability and Erosivity of Nitrogen-Rich Gun Propellants

Lavoie, Jonathan

2017

Overview

It is believed that the current approaches to energetic content in gun propellants have reached their limits. Oxidation of molecules with a carbon backbone is the approach that has been in use for decades and has reached its full potential. Strain cage structures like CL-20 provide good energetic content but remain very expensive. Additional challenges in gun propellant design include reduced sensitivity, improved thermal stability, lowered environmental impact and reducing wear of gun systems due to propellants. Nitrogen-rich materials are anticipated to be a solution to these challenges without having to sacrifice performance. However, efforts have mostly been centered on the synthesis of new molecules with little attention paid to their effects in gun propellants. This thesis aims to fill this gap in energetic materials research by measuring the effects of nitrogen-rich materials in gun propellants. More specifically, the properties investigated were the performance, stability and erosivity of nitrogen-rich propellants. A total of four nitrogen-rich materials, 5,5’-hydrazinebistetrazole (HBT), 5,5’-bis-(1H-tetrazolyl)-amine (BTA), 5-aminotetrazolium nitrate (HAT-NO3) and 3,6-dihydrazino-s-tetrazine (DHT) were incorporated at concentrations of 5%, 15%, 25% and 35% (HBT and BTA only) in a modified triple base gun propellant. The triple base was composed of nitrocellulose, trimethylolethane trinitrate and diethylene glycol dinitrate. All nitrogen-rich materials resulted in a burning rate increase regardless of concentration with the burning increase reaching as high as 93% for 5,5’-bis-(1H-tetrazolyl)-amine. Significant changes in burning rate laws also indicated changes in the combustion kinetics of the propellants which were due to the nitrogen-rich materials. The thermal stability, both short-term and long-term, was evaluated for all propellants. BTA and HBT proved to have no significant effect on the long-term stability of the propellants and the short-term thermal stability of the propellants incorporating these materials remained within acceptable levels. Both DHT and HAT-NO3 proved to have poor long-term stability. The decrease of the stability of the propellant incorporating HAT-NO3 is attributed to the salt dissociating into its acid-base precursors which leads to accelerated decomposition of nitrocellulose due to nitric acid. Propellants incorporating DHT exhibited a catastrophic autocatalytic decomposition behavior. This behavior is attributed to the decomposition products of the other materials in the propellant oxidizing DHT which leads to its decomposition and further decomposition of the propellant. The effects of HBT and BTA on the erosivity of gun propellants were characterized, a first for nitrogen-rich materials in propellants. The addition of nitrogen-rich materials significantly lowered the erosivity of the propellants. It also demonstrated that current modeling of erosion may not be adequate for nitrogen-rich materials given their semi-empirical nature and the effects of nitrogen gas diffusing and reacting with the gun steel. Finally, a set of heuristics based on the results obtained is proposed to help formulators with the initial screening of nitrogen-rich materials in gun propellant applications. These heuristics are proposed in lieu of models as it was discovered that such models could only be the result of a complex and important series of experimental works outside of the scope of a single PhD thesis.

• Publisher: ProQuest Dissertations & Theses
• Subject: Chemical engineering
• ISBN: 9798209777328