Chemistry Reference
In-Depth Information
Fig. 2.42
57
Fe Mössbauer
spectra of various corrosion
products which may be
formed under different
conditions. The spectra are
discussed in the text
slightly different size of the internal magnetic field. The oxyhydroxides a-, b- and
c-FeOOH can be distinguished by temperature dependent Mössbauer spectros-
copy. While a-FeOOH (Goethite) shows a magnetically split sextet at room
temperature, b- and c-FeOOH have the same poorly resolved quadrupole doublet
and therefore cannot be distinguished at room temperature. At liquid nitrogen
temperature (ca. 80 K), however, b-FeOOH is magnetically ordered and shows the
typical magnetically split sextet, whereas c-FeOOH still shows the same poorly
resolved quadrupole doublet as at 295 K. This phase orders magnetically only
below ca. 30 K yielding then a similar sextet as the other modifications. Thus,
Mössbauer spectroscopy enables one to distinguish between these corrosion
products, even in the form of highly dispersed particles ([ca. 10 nm), where
powder X-ray diffraction measurements are no longer applicable.
Figure
2.43
shows an example of routine Mössbauer analysis of finely dispersed
particles formed in the cooling system of a power plant. The particles were col-
lected
from
the
coolant
with
a
special
filter
and
analyzed
with
standard
Fig. 2.43 Routine Mössbauer analysis of finely dispersed corrosion particles formed in the
cooling system of a power plant [
76
]
