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Fe, Al
Fe, Al
Fe, Al
(a)
(a)
Al
Al
Al
Al
Al
Al
Fe, Al
Fe, Al
Fe, Al
Fe
Fe
Fe
(c)
(c)
(b)
(b)
Fe
Fe
Fe
20
20
20
30
30
30
40
40
40
20
20
20
30
30
30
40
40
40
50
50
50
60
60
60
70
70
70
80
80
80
2
2
2
θ
θ
θ
Figure 7.2
XRD pattern for (a) fresh bimetallic Fe/Al particles, (b) reacted bimetallic
Fe/Al particles and (c) aluminum hydroxide (bayerite).
After reacting with 31.7 mg/L CCl
4
for 24 h, bimetallic Fe/Al particles showed a
significant change in their composition at the surface (Figure 7.2(b)). The diffraction
peaks at only 44.7° and 65.0°, and the characteristic peaks assigned to aluminum were
disappeared. This indicated that ZVI was the primary species dominating at the metal
surface. Furthermore, it was found that common crystalline iron oxides such as
magnetite, maghemite, and hematite observed in iron-mediated reactions were not
detected here (Ponder et al., 2000; Lien et al., 2007). This suggested that the use of
aluminum as a core metal successfully maintains a fresh surface of iron. The
disappearance of aluminum diffraction peaks indicated the aluminum at the particle
surface was consumed during the reaction with water. Aluminum shows a strong
tendency to donate electrons, yielding dissolved aluminum ions (Eq. 7.2) that are
subsequently formed a passive layer of aluminum hydroxide to prevent a further
oxidation of aluminum (Eq. 7.3):
Al
0
→
Al
3
+
+
3e
-
(Eq. 7.2)
Al
3
+
+
3OH
-
→
Al(OH)
(Eq. 7.3)
3
The crystallization of aluminum hydroxide/oxyhydroxides is a slow process that
causes an either amorphous or poorly crystalline structure in most aluminum
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