Transmission Electron Microscopy of Synthetic 2- and 6-Line Ferrihydrite

Abstract

Abstraet~High-resolution transmission electron microscopy (HRTEM), selected-area electron diffraction (SAED), annular dark-field scanning transmission electron microscope (STEM) images, and electron nanodiffraction were used to examine structures of synthetic 2-and 6-line ferrihydrite specimens. 086, 0.093, 0.107, 0.112, 0.119, 0.125, and 0.135 nm are visible in strongly exposed SAED patterns. Small quantities of hematite, magnetite or maghemite, and an acicular material tentatively identified as goethite were observed in the 6-line ferrihydrite, but these quantities do not contribute significantly to the overall diffracted intensity from the sample.

Characterization of the pores in hydrous ferric oxide aggregates formed by freezing and thawing

“…One can clearly observe the unit crystallites of the HFO, which are estimated to be 1.9 ±0.5 nm in diameter. This size is in good agreement with data published by Janney and co-workers [36] for a two-line HFO synthesized using a similar procedure. Fig.…”

Transformation of 2-line ferrihydrite to 6-line ferrihydrite under oxic and anoxic conditions

“…The crystallites exhibited lattice fringes consistent with 6-line ferrihydrite at 0.25 nm and 0.285 nm. The crystallite morphology was similar to that of the 6-line ferrihydrite reported by Janney et al (2000). An SAED pattern of these crystals ( Fig.…”

“…An SAED pattern of these crystals ( Fig. 3b) displayed d values (for the diffuse rings) that were within errors of determination from those reported for 6-line ferrihydrite (Janney et al 2000).…”

“…4a) and did not exhibit coherent domains. The SAED pattern displayed two bright rings with shoulders on each side, identical to the 2-line ferrihydrite of Janney et al (2000). In addition to the 2-and 6-line ferrihydrite, the micrographs displayed regions that were rich in acicular goethite crystals (~30 nm long, top right corner, Fig.…”

Nanoparticles in natural systems I: The effective reactive surface area of the natural oxide fraction in field samples

“…Most samples in our study have an effective particle size that is typical for synthetic ferrihydrites. For instance, the particle size of freshly prepared two-line ferrihydrite varies between about 1.5 and 3.0 nm (Murphy et al, 1976), while for 6-line ferrihydrite the numbers are about 5-7 nm (Janney et al, 2000). Some of our samples have a very high effective SSA and the corresponding effective particle size is extremely low (about 1 nm).…”