Scanning Electron Microscopy and X-Ray Microanalysis

476

27

the damage seen in. Fig. 27.6. (Note that the practical solu-

tion to this problem was to modify the wire connections to

provide much greater springiness to eliminate the opening of

gaps that allowed arcing to occur.)

27.3 Case Study: Characterizing

the Microstructure of a Manganese

Nodule

“Manganese nodules” are rock concretions that form on the

deep sea floor through the action of microorganisms that

precipitate solid chemical forms from metals dissolved in the

water, often in close association with hydrothermal vents.

The elemental composition of a polished cross section of a

manganese nodule, shown in. Fig. 27.11, was examined by

SEM/BSE and by SEM/EDS X-ray spectrum imaging elemental

mapping. The SEM/BSE image in. Fig. 27.12 reveals a complex

layered microstructure that suggests non-uniform deposition

of the precipitated minerals over time. This non- uniform depo-

sition is confirmed by the elemental maps for O, Mn, and Ni

and color overlay shown in. Fig. 27.13 and for the Mn, Fe, and

Ni maps shown in. Fig. 27.14. Note the oxygen- rich areas

(green) in. Fig. 27.13. These regions correspond to silica and

aluminosilicate grains within the manganese nodule, as revealed

in. Fig. 27.15. The composition measured with a fixed beam

placed at the center of the field of view is listed in. Table 27.1,

showing the high abundance of Mn as a major constituent and

the presence of other transition elements (e.g., Fe, Ni, and Cu)

as minor constituents.. Figure 27.16 shows the results of quan-

titative processing of the XSI with the k-ratio/matrix correction

protocol using DTSA-II.  The resulting concentration maps

have been encoded with the logarithmic three- band color

scheme shown in. Fig. 27.16, enabling quantitative compari-

son of the constituents, using NIST Lispix.

Note that some features in the elemental maps are a result

of artifacts. Thus, the cracks noted in the SEM/BSE of

. Fig. 27.11 are also seen in the O elemental map, but not in
the Mn or Ni maps. The origin of this artifact is the difference
in the photon energies of these elements. The O K-shell X-ray

Al 0.759 a/o

Fe 0.241 a/o

FeAl 3

Al 0.719 a/o

Fe 0.281 a/o

Fe 2 Al 5

Mounting

epoxy

Steel

screw

. Fig. 27.10 SEM-BSE image of
the anomalous zone of contact
with quantitative X-ray micro-
analysis results from fixed-beam
analysis in the two distinct Al-Fe
regions (note the contrast in the
BSE image)
. Fig. 27.11 Manganese nodule

Chapter 27 · X-Ray Microanalysis Case Studies