Properties of a gas-generating composition related to the particle size of the oxidizer

In general generators are defined as devices which produce gas force or power in the form of gas. In the present work we will focus on cold gas generators actuated by pyrotechnics. These gas generators are often applied for pressurizing or inflating systems in which high temperatures are not acceptable. Typical applications are: airbags, seat-belt tensioners, fire extinguishers. Depending on the application, gas-generating materials have to fulfil a series of requirements, such as goo,d performance reproducibility, easy and reliable ignition, low explosion temperature, high yield of gas, low yield of condensed products, specific gas composition, and adequate burning rate and vivacity. In previous work a whole range of possibly suitable single compounds, such as sodium azide, double base propellant, azodicarbonamide, guanidine derivatives and azole derivatives were studied. These compounds - whether or not stoichiometrically mixed with an oxidizer (e.g. KNO₃, KClO₄ or NH₄NO₃) - were theoretically and experimentally examined in order to evaluate their combustion properties. The objective of this work is to experimentally investigate the influence of the particle size of an oxidizer on the combustion behavior of a gas-generating pyrotechnic mixture. As an example a series of nitroguanidine (NQ)/potassium nitrate (KNO₃)mixtures with well-defined KNO₃-particle size fractions are selected. Raman spectroscopy is used to examine the constituent distribution within the bulk and thus the mixing efficiency. Closed vessel tests are used to experimentally compare ignition delay, burning rate, dynamic vivacity, and yield of gas. The composition of the combustion gases is examined through gas analysis. The experiments show that a decrease of the particle size of the KNO₃particles has a positive influence on the mixing efficiency and on the investigated combustion properties of a NQ/KNO₃-composition. The combustion process of this mixture becomes better controllable when a small KNO₃-particle size fraction is selected, but its combustion behavior is comparable to that of a NQ/KNO₃mixture containing a broad KNO₃-particle size distribution.