Combustion properties of gas-generating pyrotechnics

This work focuses particularly on solid energetic materials designed to produce high-pressure gas for pressurizing or inflating devices. In cool gas generators sodium azide is often used. Unfortunately, this chemical exhibits drawbacks concerning toxicity and yield of gas. Another gas-generating agent is double base propellant, which has traditionally been used in the rocket-industry. However, it delivers toxic and reactive gases and its combustion temperature is high. In previous work a series of gas-generating materials have been proposed as potential alternatives fueled with double base propellant, azodicarbonamide, nitroguanidine, or guanidine nitrate and stoichiometricly oxidized with potassium nitrate or potassium perchlorate. The purpose of this paper is to examine and compare the burning characteristics of the previously proposed compositions. To carry out this characterization, methods typical for propellant technology are used. Ignition delay, time from ignition to maximum pressure, burning rate, and absolute vivacity have been investigated through closed vessel tests. Thanks to the use of a gaseous ignition mixture the form function of the tested grains is not deteriorated. This leads to fairly reproducible results for the burning rate and the absolute vivacity, despite possible discrepancies in the ignition delay. In most of the studied cases, the addition of an oxidizer tends to improve the ignition delay and the time from ignition to maximum pressure. In addition the burning rate and absolute vivacity increase significantly. The only exception is double base propellant, where the presence of an oxidizer causes relatively minor changes in its combustion properties.