Biomedical Engineering Reference
In-Depth Information
Table 10.7
Calcium phosphate phases. Data collated from [340, 341]
Notation
mol L
1
Formula
Ca/P
log
K
sp
MCPM
Ca(H
2
PO
4
)
2
.H
2
O
DCP
CaHPO
4
1
6:9
DCPD
CaHPO
4
.2H
2
O
1
6:6
OCP
Ca
8
(HPO
4
)
2
(PO
4
).5H
2
O
1.33
72:5
WH
Ca(MgFe)
10
(HPO
4
)(HPO
4
)
6
1.43
81:7
TCP
Ca
3
(PO
4
)
2
1.50
28:6
OHA,HAP,HA
Ca
10
(PO
4
)
6
(OH)
2
1.67
117:1
DOHA
Ca
10
u
(HPO
4
)
u
(PO
4
)
6
u
(OH)
2
u
(10
u)/6
85:1
and the third is very weak. For all practical purposes, the concentrations of the ions
figuring in the equations of thermodynamic constants should be corrected for all
reactions compromising the active concentrations (protolysis, complex formation,
activitycoefficients...)asdiscussedatsomelengthinthechaptersoncorrosionand
toxicity (
conditional constants
).
The notations used in Table
10.7
refer to:
<
MCPM: monocalcium phosphate monohydrate.
DCP(A): dicalcium orthophosphate (anhydrous); 'ortho-'because derived from a
reaction of Ca(OH)
2
with orthophosphoric acid (IUPAC nomenclature). Mineral
name: Monetite. Occurs in nature as a tan coating on a magnesium phosphate
(newberyite).
DCPD: idem but crystallized with 2 molecules of water.
OCP*: octacalcium (ortho)phosphate.
WH**: mineral name Whitlockite. Occurs in nature and is prominently present
in lunar rocks.
TCP:
ˇ
-tricalcium (ortho)phosphate;
˛
-tricalcium phosphate.
HA(P): calcium hydroxyapatite. Trivial name.
DOHA or (C)DHA: (calcium)-defective apatites,
. HAP as mineral or
biomineral is almost never simply stoechiometric and/or well crystallized. OH
may partially be substituted by fluor, carbonate or chloride, Ca
2C
by Mg
2C
.
0
u
2
TTCP: tetracalcium phosphate.
KCA:
*OCP is a somewhat elusive compound. It might be formed from precipitated
amorphous calcium phosphate (Ca/P
1.45) and may serve as template for the crys-
tallization of HAP (a statement formulated many decades ago!). **An amorphous
calcium phosphate (ACP) might be the precursor of DOHA and is considered as
being WH with colloidal dimensions.
When
IP
of a supersaturated solution exceeds for a given compound, the condi-
tional solubility product, which is as a matter of fact the equilibrium value of
IP
,
the compound will start to precipitate, a due consequence of our thermodynamic
slogan
water does not flow uphill
. The Gibbs-free energy difference
D
G
between
solution and solid acts as the driving force:
