Comparison of engineered nanocoatings on the combustion of aluminum and copper oxide nanothermites

Water-repellent nano-coatings for submerged combustion of nano-energetic composite materials were developed. These coatings may have applications for oceanic power generation, underwater ordnance, propulsion, metal cutting, and torch technologies. Nano-coatings were deposited on thermite pellets by a vapor-phase technique. Two types of deposition techniques studied were chemical vapor deposition (CVD) and atomic layer deposition (ALD). A total of six types of nano-coatings were applied on the thermite pellets. Various process parameters to produce the coatings were explored. Characterization of the nano-coatings was carried out using Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and contact angle goniometry. Submerged combustion tests of the nano-coated thermite pellets were performed as a function of submerged time. The pellets were submerged in de-ionized water for 3, 5, and 10 days. The energy released by the thermite reaction was analyzed and compared to other types of nano-coated pellets. Initial results of a fluorocarbon self-assembled monolayer (FSAM) coating were compared with an ALD coating composed of Al2O3. Results show that with increasing submerged time, there was a decrease in the ratio of bubble energy to total energy of combustion (Kc = Kbubble/Kcombustion) for all coatings tested. The initial bubble energy of the pellets coated with FSAM and ALD with Al2O3 was 133.3 and 142.2 (KJ/Kg), respectively. After submersion for 10 days, the bubble energy reduced to 10.4 and 15.6 (KJ/Kg), respectively. The value of Kc for the FSAM coating decreased by a factor of 12.8 whereas the ALD with Al2O3 coating decreased by a factor of 9.1. The hydrophobic coating is critical for energy generation because without it, the pellets do not ignite, resulting in 100% loss of energy.