INTERNAL STRUCTURE-ANALYSIS OF MONODISPERSED PEANUT-TYPE HEMATITE PARTICLES PRODUCED BY THE GEL-SOL METHOD

The internal structure of monodispersed peanut-type hematite (alpha-Fe2O3) particles prepared by the gel-sol method has been studied through high-resolution electron microscopy on their thin films sliced with an ultramicrotome. The electron micrographs and electron diffraction patterns of the thin sections not only directly revealed their polycrystallinity but also disclosed the shape, size distribution, and orientation of the subcrystals in detail. The subcrystals inside the particles have a rod-like shape in the range 5 to 10 nm in width and about 70 nm in length, while those at the surfaces indicate a shape like a truncated cone. The long axis of each subcrystal has been confirmed to coincide with the c-axis of the hexagonal system. Their tilt angles against the revolutional axis of a peanut-like particle were found to be enlarged as they approached both ends of the particle, suggesting the formation process of the peanut-like shape. Also, most of the added sulfate ions, as a shape controller, were incorporated into the particles, as proved by EDX analysis. By comparing the present results with the internal structures of the pseudocubic and platelet-type hematite particles prepared by the gel-sol method, the individual formation mechanisms have been discussed. (C) 1994 Academic Press, Inc.