taken through a Leica M 205C stereomicroscope, and the isotropic or anisotropic
properties (Lynn et al. 2008) of the constituents were analyzed in optical micrographs taken under a Nikon ECLIPSE E600 POL microscopic system.
The micro-scale morphological properties of soil inorganic constituents were
revealed in scanning electron microscope (SEM) (White 2008) and transmission
electron microscope (TEM) (Elsass et al. 2008) images. For SEM observation,
air-dried sample particles were held on double-sided sticky tape. Polished sections
were used to reveal the two-dimensional structures of inorganic soil particles, soil
clods, and rice–root bundles. To avoid charging, the samples were coated with
vacuum-evaporated carbon. Alternatively, Pt–Pd coating was applied if the carbon
coating was insufficient. For TEM observation, sample particles were supported on a
copper mesh by a collodion membrane. Allophane and imogolite were observed on a
TEM microgrid. TEM photographs were obtained by a Quemesa digital camera.
Both the SEM and TEM observations were carried out under high vacuum. For
morphological observation and energy dispersive X-ray (EDX) analyses
(Guillemette 2008), the accelerating voltage of the SEM was typically set to
15 kV, but it was sometimes set to 3 kV for detailed morphological observations.
Most of the SEM and TEM observations were performed on Hitachi SU8000 and
H-7650 instruments, respectively.
The elemental compositions of inorganic constituent particles and the distribution
of elements can effectively identify the particles and may reveal chemical reaction
products. This monograph presents many EDX spectra as visual examples of the
element abundances of inorganic soil constituents. Elemental compositions were
analyzed from the characteristic X-ray spectra of the samples (Fig. 1.2) obtained by
EDX. Metals heavier than Fe are rare among the inorganic constituents of most soils.
The relative abundances of the elements can be roughly estimated from the heights
of the peaks of the characteristic X-rays in the spectra although the elemental
composition is accurately calculated in quantitative analysis using an equipped
software. In early work, EDX analyses were usually performed on a Kevex apparatus, but more recent analyses were performed using an EDAX Apollo XV.
Points of attention for EDX analytical results include overlapping of characteristic X-rays, the position of the X-ray detector, and some others. Among the
overlapping of characteristic X-rays mentioned in the EDX manual, FK α – FeL α
and PK α – ZrL α may sometimes be encountered when observing inorganic constituents in soil. As the X-ray detector is installed diagonally upward from the sample,
unevenness in the sample surface affects the effectiveness of the detector for
detecting characteristic X-rays, and the X-ray intensity from the opposite side of
the sample is weak. Also, shadows are formed in the element maps of particle
samples of soil inorganic constituents. To avoid the effects of uneven samples, it
is necessary to use adequately flat or polished sections with soil inorganic constituents embedded in resin.
X-ray diffraction patterns of powder samples were acquired by a Rigaku
MiniFlex X-ray diffractometer using the CuK α (30 kV, 15 mA) line at a scanning
speed of 2
per minute. For this purpose, oriented samples were prepared on glass
slides using Mg
2+ - and K
+
-saturated samples at room temperature, and their X-ray
6
1 Purpose and Scope
properties (Lynn et al. 2008) of the constituents were analyzed in optical micrographs taken under a Nikon ECLIPSE E600 POL microscopic system.
The micro-scale morphological properties of soil inorganic constituents were
revealed in scanning electron microscope (SEM) (White 2008) and transmission
electron microscope (TEM) (Elsass et al. 2008) images. For SEM observation,
air-dried sample particles were held on double-sided sticky tape. Polished sections
were used to reveal the two-dimensional structures of inorganic soil particles, soil
clods, and rice–root bundles. To avoid charging, the samples were coated with
vacuum-evaporated carbon. Alternatively, Pt–Pd coating was applied if the carbon
coating was insufficient. For TEM observation, sample particles were supported on a
copper mesh by a collodion membrane. Allophane and imogolite were observed on a
TEM microgrid. TEM photographs were obtained by a Quemesa digital camera.
Both the SEM and TEM observations were carried out under high vacuum. For
morphological observation and energy dispersive X-ray (EDX) analyses
(Guillemette 2008), the accelerating voltage of the SEM was typically set to
15 kV, but it was sometimes set to 3 kV for detailed morphological observations.
Most of the SEM and TEM observations were performed on Hitachi SU8000 and
H-7650 instruments, respectively.
The elemental compositions of inorganic constituent particles and the distribution
of elements can effectively identify the particles and may reveal chemical reaction
products. This monograph presents many EDX spectra as visual examples of the
element abundances of inorganic soil constituents. Elemental compositions were
analyzed from the characteristic X-ray spectra of the samples (Fig. 1.2) obtained by
EDX. Metals heavier than Fe are rare among the inorganic constituents of most soils.
The relative abundances of the elements can be roughly estimated from the heights
of the peaks of the characteristic X-rays in the spectra although the elemental
composition is accurately calculated in quantitative analysis using an equipped
software. In early work, EDX analyses were usually performed on a Kevex apparatus, but more recent analyses were performed using an EDAX Apollo XV.
Points of attention for EDX analytical results include overlapping of characteristic X-rays, the position of the X-ray detector, and some others. Among the
overlapping of characteristic X-rays mentioned in the EDX manual, FK α – FeL α
and PK α – ZrL α may sometimes be encountered when observing inorganic constituents in soil. As the X-ray detector is installed diagonally upward from the sample,
unevenness in the sample surface affects the effectiveness of the detector for
detecting characteristic X-rays, and the X-ray intensity from the opposite side of
the sample is weak. Also, shadows are formed in the element maps of particle
samples of soil inorganic constituents. To avoid the effects of uneven samples, it
is necessary to use adequately flat or polished sections with soil inorganic constituents embedded in resin.
X-ray diffraction patterns of powder samples were acquired by a Rigaku
MiniFlex X-ray diffractometer using the CuK α (30 kV, 15 mA) line at a scanning
speed of 2
per minute. For this purpose, oriented samples were prepared on glass
slides using Mg
2+ - and K
+
-saturated samples at room temperature, and their X-ray
6
1 Purpose and Scope