Generation and use of three types of iron-oxide aerosol.

Three distinct submicrometric aerosols of iron oxide can be reproducibly generated by combustion of iron pentacarbonyl vapors under varying conditions. Each aerosol was sized with a concentric aerosol spectrometer and was examined with an electron microscope; the specific surface area of each aerosol type was also determined. The "feathers" hematite has a man median aerodynamic diameter (MMAD) of 0.17 micrometer and a large surface area because it is an agglomerate of units 0.005 micrometer in diameter. The "birdshot" hematite has a MMAD of 0.31 micrometer, but has a smaller surface area because the subunits are 0.03 micrometer in diameter. The third aerosol, "gamma-oxide," has a MMAD of 0.73 micrometer and has crystalline subunits 0.2 micrometer in diameter; it is a magnetic form of hematite, gamma-Fe2O3. These aerosols are well suited for studies of deposition and clearance in animal lungs because the particles can be visualized in both light and electron microscopy and can be quantified colorimetrically. The magnetic properties of gamma-Fe2O3 permit enhancement of deposition and noninvasive detection.