Moessbauer parameters for ferrihydrites at 4 K

Abstract

The Moessbauer spectra at 4.2K for five ferrihydrites (one natural, four synthetic) have been determined. Two of the samples contained silicon (atomic ratio Si/Fe= 18%, 21%) and one contained aluminium (Al/Fe = 19%). The Moessbauer parameters were calculated from peak positions estimated by a fit of one set of six Lorentzian lines to each spectrum and by judging absorption maxima by eye. Hyperfine magnetic field (H) values were between 50.0 and 50.4 T for pure samples and between 48.3 and 49.2 T for samples containing silicon or aluminium. Variations as small as these, due to impurities, would not prevent ferrihydrite being distinguished from lepidocrocite (H= 46.0 � 0.5 T for pure, well-crystallized material) in Moessbauer spectra of soil samples at 4.2 K.

The nature of an iron oxide—organic iron association in a peaty environment

“…In spite of the differences in hyperfine field distributions, the M6ssbauer spectra of all these samples are consistent with ferrihydrite being the major Fe-bearing constituent, the magnetic properties of ferrihydrite being known to vary noticeably with crystallinity (Murad & Schwertmann, 1980; and/or chemical composition (Childs et al, 1984). However, because of the indefinite XRD data, the residue of the oxalate treatment must be excluded from this discussion.…”

Geochemistry of iron and manganese in soils and sediments of a mangrove system, Island of Pai Matos (Cananeia — SP, Brazil)

“…Murad and Schwertmann (1980) reported that the hyperfine field of lepidocrocite at 4.2 K is 45.8 T, and Vandenberghe et al (1990) reported it to be between 44 and 46 T. Site 4 (11%) could therefore be assigned to lepidocrocite (Table 2). At 4 K, the hyperfine field of ferrihydrite is 48.4 T (Murad and Schwertmann (1980) or between 48.3 and 50.4 T (Childs et al, 1984). In the same study (Childs et al, 1984) the isomer shift varied between 0.48 to 0.57 mm/s.…”

“…At 4 K, the hyperfine field of ferrihydrite is 48.4 T (Murad and Schwertmann (1980) or between 48.3 and 50.4 T (Childs et al, 1984). In the same study (Childs et al, 1984) the isomer shift varied between 0.48 to 0.57 mm/s. Comparison of these values with the site 3 values shown in Table 2, indicates that site 3 (18%) could be assigned to ferrihydrite.…”

Comparative mineralogy and geochemistry of hydrothermal iron‐rich crusts from the Pitcairn, Teahitia‐mehetia, and Macdonald hot spot areas of the S. W. pacific

“…The present <T B > values between 40 and 12 °K therefore imply a mean particle size in the range of 3-4 nm. The inclusion of Si in the lattice, which is likely to occur on precipitation of iron oxyhydroxides in seawater, will reduce the value of <T B > (Childs et al, 1984;Chadwick et al, 1986). The mean particle size is therefore probably somewhat larger than 3-4 nm, but this cannot be accurately quantified.…”