Gas-phase flame synthesis and characterization of iron oxide nanoparticles for use in a health effects study

Iron oxide nanoparticles, to be used in a health effects study, were synthesized in a H2/air diffusion flame and characterized by transmission electron microscopy, X-ray diffraction, surface area measurement, inductively coupled plasma mass spectrometry, and a spectrophotometric speciation method. The nanoparticles exhibited the maghemite (gamma-Fe2O3) crystal structure and contained only trivalent iron. There were two size modes in the particles. The large size mode contained crystalline, non-agglomerated particles with a median diameter of approximately 45 nm; the small size mode contained particles that were in the size range of 3-8 nm and were mostly amorphous. Depending on the value taken for the small particle size, the small mode accounted for 73-82% of the particle surface area. The particles in the small size mode were likely formed from the vapor of FeO and Fe.