Biomedical Engineering Reference
In-Depth Information
pastes. Besides, mCPm might be added to ceramics and glasses,
while agriculture is the main consumer of a technical grade mCPm,
where it is used as a fertilizer [36, 134].
1.3.2
MCPA (or MCP)
; the chemically
correct name is calcium dihydrogen orthophosphate anhydrous)
is the anhydrous form of mCPm. It crystallizes under the same
conditions as mCPm but at temperatures above ~100°C (e.g., from
highly concentrated mother liquors during fertilizer production).
like mCPm, mCPA never appears in calcified tissues and is not
biocompatible due to its acidity. There is no current application of
mCPA in medicine. Due to the similarity with mCPm, in many cases,
mCPA might be used instead of mCPm [36, 134]; however, highly
hydroscopic properties of mCPA reduce its commercial application.
monocalcium phosphate anhydrous (Ca(H
PO
)
2
4
2
1.3.3
DCPD
O; the chemically
correct name is calcium hydrogen orthophosphate dihydrate; the
mineral brushite [136]) can be easily crystallized from aqueous
solutions at ~2.0 < pH < ~6.5. Interestingly, but precipitation of
DCPD by mixing a Ca(OH)
Dicalcium phosphate dihydrate (CaHPO
·2H
4
2
solution in the
equimolar quantities was found to occur in five stages, being HA the
first precipitated phase [137, 138]. Besides, DCPD might be prepared
in gels [139, 140]. DCPD transforms into DCPA at temperatures above
~80°C and this transformation is accompanied by ~11% increase in
volume [141] and structural changes [142]. The value for Δ
suspension and a H
PO
2
3
4
G
0
for
r
Æ
DCPD
DCPA transformation is −1.032 kJ/mol [142]. Briefly, DCPD
crystals consist of CaPO
chains arranged parallel to each other,
while lattice water molecules are interlayered between them. Using
surface X-ray diffraction, Arsic et al. determined the atomic structure
of the {010} interface of DCPD with water [143, 144]. Since DCPD
contains water layers as part of its crystal structure, special ordering
properties at the interface are expected. This interface consists of
two water bilayers with different ordering properties. The first is
highly ordered and can be considered as part of the DCPD crystal
structure. Surprisingly, the second water bilayer exhibits no in-plane
order but shows only layering in the perpendicular direction. It has
4
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