Biomedical Engineering Reference
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principles of fabrication are shown in Section 5.3.2,
in which the compact oxide layer or barrier layer is
explained in details (see also Section 5.3.1).
(ii)
synthesized by a sol-gel method: Particularly,
the formation of microparticles prepared by a
microemulsion technique. As a precursor's titanium
isopropoxide,
TiO
2
(2-
ethylhexyl) sulfosuccinate (AOT from Sigma),
hexane, and water were used as received. Titanium
isopropoxide was added to an AOT/hexano/water
microemulsion to initiate the synthesis. First, 3 mL of
titanium isoproposide was mixed with 15 mL of hexane
followed by stirring at room temperature for 30 min.
Then, the microemulsion was formed by adding 3 mL
of water to a mixture made of 15 mL of AOT and hexane
followed by sonication and stirring for 1 h. Finally, we
added drop by drop the solution containing AOT + H
anionic
surfactant
sodium
bis
O
to the solution composed of titanium isopropoxide.
The resultant solution was stirred and sonicated for
1 h. To separate the formed solid from the aqueous
solution, the mixture was washed with distilled water
by spinning it repeatedly. The powder was then dried
and cured at room temperature for 24 h. Afterward, the
obtained precursor was successively heated at 100°C,
200°C, 300°C, and 450°C.
From Fig. 5.18, it is apparent that the presence of nanotubes
leads to a significant improvement of the areal capacity compared
with compact layer and micro-TiO
2
2
elaborated by a reverse micelle
synthesis (R.M.S.). Amorphous titania compact layer exhibits areal
capacity about 20
μ
in first discharge. Meanwhile, the
first reversible capacity is about 10
Ah cm
-
2
μ
, and this value is
almost kept after 50 cycles. On the other hand, the areal capacities
values of micro-TiO
2
Ah cm
-
2
at 100°C, 300°C, and 450°C are 30, 40, and
μ
, respectively. On cycling, the capacity retention is very
poor (less than 20
37
Ah cm
-
2
μ
after 10 cycles), except for sample
heated at 450ºC, which retains the capacity slightly better and
after 35 cycles exhibits about 15
Ah cm
-
2
μ
Ah cm
-
2
. We have fabricated an
amorphous TiO
2
nanotube layer that presents high areal capacity
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