Burning Rate Characterization of Guanidine Nitrate and Basic Copper Nitrate Gas Generants with Metal Oxide Additives
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Automotive airbag gas generants have been studied extensively to create formulations that meet both inflation and safety requirements. Additives have been used to increase the burning rates of these propellants, but the additive size has not been investigated. This thesis established the capability of studying such propellants at Texas A&M University for the first time and compared nano- and micron-sized additive burning rates and combustion characterization in guanidine nitrate (GN) and basic copper nitrate (BCN) composite propellants. Three metal oxide additives were chosen for this study: aluminum oxide (Alv2Ov3), ceria (CeOv2), and titania (TiOv2). They were tested in both their nano- and micron-sized forms at a mass loading of 4% to determine burning rate characterization differences. Formulations were mixed using a Resodyn acoustic mixer, and the samples were prepared using a hydraulic press. Resulting cylindrical pellets were then inhibited and burned over a range of pressures from 1000 psi (6.9 MPa) to 4000 psi (27.6 MPa). Results from the burning rate experiments yielded in all formulations that the micron-sized additives performed better than their nano-sized counterparts. Also, all formulations except micron ceria performed worse than the stoichiometric GN/BCN baseline propellant. From the very different slag recovered from the burned propellants containing each additive, it was clear that the additives were affecting the propellant in different ways. It was concluded that due to the wide particle size range of the BCN used in this thesis, fewer catalytic reaction zones were being created for the nano-sized particles, causing the additive to remove heat from the main GN/BCN reaction and ultimately inhibiting burning. The micron-sized additives removed heat to a lesser extent since they produced more catalyzed reaction zones when the small-sized BCN particles coated the additives. Future testing should focus on controlling the fuel and oxidizer size distribution to have more definitive results.
