Using a rapid, open-atmosphere flame synthesis technique, iron-oxide nanoparticles (alpha-Fe2O3) and nanocrystals (gamma-Fe2O3) and carbon nanotubes (CNTs) are grown directly on stainless steel substrates. Multiple inverse-diffusion flames provide both oxide species (H2O and CO2) and carbon species (CH4, CO, C2H2), at elevated temperature, conducive for the growths of iron-oxide nanoparticles/nanocrystals and CNTs. The growth of alpha-Fe2O3 nanoparticles occurs at 500 degrees C. At a temperature of 850 degrees C, the growth of CNTs occurs on type 304 stainless steel, while gamma-Fe2O nanocrystal films are grown on 304 L and 316 L stainless steels with relatively lower innate carbon content. Interestingly, a temperature-step process, where 304 stainless steel substrate is initially at 500 degrees C and then increased to 850 degrees C, distinctly converts the "seed" alpha-Fe2O3 nanoparticles into larger gamma-Fe2O3 nanocrystals, with some scattered CNTs. Strategically time-varied local conditions should produce different compositional ratios of iron-oxide/CNT hybrid films, as well as targeted functionally-graded nanostructures and nanocomposites. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
