SnO2 atomic layer deposition on ZrO2 and Al nanoparticles: Pathway to enhanced thermite materials

Thermite mixtures with improved contact between the fuel and oxidizer can provide increased reaction rates compared with traditional thermite mixtures. One technique to create thermite mixtures with improved contact is to deposit the oxidizer directly onto nanometer-sized fuel particles. This study investigates the atomic layer deposition (ALD) of SnO2 onto nanoparticles using SnCl4 and H2O2 reactants. The nanoparticle ALD was performed in a small, hot wall, vertical fluidized bed reactor. The SnO2 ALD was first demonstrated on ZrO2 nanoparticles. Auger electron spectroscopy, inductively coupled plasma-atomic emission spectroscopy (ICP-AES), transmission electron microscopy (TEM) and particle size distribution analysis were used to characterize the SnO2-coated ZrO2 nanoparticles. Subsequently, SnO2 ALD was performed on Al nanoparticles. The SnO2-coated Al nanoparticles were analyzed using ICP-AES and TEM. The SnO2-coated Al and the uncoated Al particles were also ignited and filmed with a digital video recorder. Although the SnO2-coated Al particles were far from stoichiometric thermite composites, the SnO2-coated Al particles reacted much more quickly and violently than the uncoated Al particles. The lower than expected Sn percent by mass observed on the SnO2-coated Al nanoparticles highlighted a major difficulty with coating nanoparticles. The nanoparticles have an extremely high surface area and the required reactant exposures are large even when assuming 100% reactant efficiency. These results illustrate the utility of ALD techniques to coat oxidizers on fuel nanoparticles to create enhanced thermite materials.