Environmental Engineering Reference
In-Depth Information
The magnetic properties of Al-doped -Fe
2
O
3
with various molar ratios of Al
were measured by VAM. Figure 9.12 illustrates typical magnetization loops for the Al-
doped -Fe
2
O
3
, where no reduced remanence and coercivity were observed. The
magnetic hyperfine field of -Fe
2
O
3
decreased with increasing incorporation of the non-
magnetic aluminum. Especially for Al-doped -Fe
2
O
3
with an Al/(Al + Fe) of 13.1%, the
saturation moment cannot be obtained under the applied magnetic field strength. The
surface area and magnetic properties are summarized in Table 9.2. One can see that the
surface area of Al-doped -Fe
2
O
3
nanoparticles increased with the dosage of Al-dopant.
The Al
3+
is slightly smaller than that of the Fe
3+
, 0.53 Å vs. 0.64 Å (Shannon and Prewitt,
1969). Thus, the average size of the unit cell of the Al-doped -Fe
2
O
3
decreases.
Similarly, Thiel (1963) studied Al-substituted goethites synthesized under hydrothermal
conditions at high pH and found that d(111) and the unit-cell dimensions decreased
linearly with Al substitution.
Figure 9.13
Magnetic moment vs. applied magnetic field.
Table 9.2
Magnetization and surface area for various Al-doped -Fe
2
O
3
.
Al/(Al + Fe(III))
Surface Area
Magnetic Properties
(m
2
/g)
(mol %)
(emu)
0.0
162
3.48
7.5
182
2.26
9.3
191
1.65
11.0
198
1.14
13.1
210
/
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