Biomedical Engineering Reference
In-Depth Information
Fig. 6.4
Optical properties of the composite consisting of CaCO
3
and PAA in the bulk state.
(
a
) Macroscopic appearance of the bulk state. (
b
) Optical microscopy (upper) and its cross-
polarized optical microscopy (lower) images, respectively. (Reproduced from [
54
], Copyright
© 2008, Wiley VCH)
6.2.2
Gas Diffusion Technique
The ACC can be obtained by using ethanolic CaCl
2
and ammonium carbonate as
the sources of calcium and carbon dioxide, respectively [
56
]. Other additives or any
elaborating pH control are not necessary to form the precursor of ACC. Ethanol
itself inhibits the dissolution of ACC so that the solution mediated phase transition
of ACC to calcite or vaterite can barely take place. The calcium carbonate precipitate
(CCP) was synthesized in 10 mM ethanolic CaCl
2
solution by allowing the diffusion
of CO
2
vapor from (NH
4
)
2
CO
3
into the solution; the whole reaction vessel was
kept at 293 K using a water-circulating temperature controller. When the reaction
is carried out, the solution phase became milky-white and then a white gel-like
precipitate was deposited at the bottom. After 1 day, the reaction finished and the
gel-like precipitate was filtered out. The obtained precipitate is called CCP. When
the CCP is heated to 373 K for 24 h in a N
2
atmosphere flowing at 110 mL min
1
,
the ACC is obtained (Fig.
6.5
)[
56
].
Interestingly, Gower and co-workers reported that the polyaspartic acid is
important for the formation of the ACC phase [
57
]. Furthermore, the PILP (polymer-
induced liquid- precursor) process results in the formation of an amorphous
phase which is induced and stabilized by a polymeric additive. The subsequent
crystallization of the deposited film produces calcitic tablets similar in shape to
the nacreous tablets. This PILP process was used elsewhere to grow a calcium
carbonate amorphous film at a fatty acid monolayer located at an air-water interface.
The vapor diffusion method that we commonly use to form the PILP droplets was
scaled up to generate sufficient phase for compositional analysis. The experimental
