Geoscience Reference
In-Depth Information
Table 5.16 Physicochemical Properties of Synthetic Hydrothermal or Natural FAp
[204]
Properties
Values
Comments
Theoretical formula
Ca
10
(PO
4
)
6
(OH)
2
Composition varies with sample
preparation
mono.
2
hexa. transition may occur
at ca. 200
C
Space group
P6
3/m
(hexagonal)
P2
1/b
(monoclinic)
a
5
9.41
9.44
˚
Lattice parameters (LP)
Large discrepancies in LP of “Wet
chemically” HAp
6.94
˚
c
5
6.84
3.16 g/cm
3
Theoretical density
Varies with composition
Moh's hardness
3(CO
3
-Ap)
Water and CO
3
in apatite lattice lower
hardness
5(HAp)
Heat capacity
184.07 cal/K mol at
298.16 K 950
C
“Wet” HAp following calcined at
“wet” HAp following calcined at
1100
C
180.16 cal/K mol at
298.15 K
11
14
3
10
2
6
K
2
1
Thermal expansion
coefficient
“wet” HAp expands nonlinearly
1614
C
Melting point
“synthetic” HAp, hot-stage microscope
method
Surface energy
S(001)
5
95
6
25 MPa
Natural FAp, slow cleavage method
Stiffness coefficient at room
temperature (mbars)
C11
5
1.434,
C33
5
1.805
Natural FAp, ultrasonic pulse
superposition
C44
5
0.415,
C12
5
0.445
C13
5
0.575,
C66
5
0.495
7.40
10.47
Dielectric constant
Varies with composition
n
w
5
l.649
1.651,
n
c
5
l.642
1.644
Refractive indices
relationship between indices and
composition is shown in Ref.
[1]
.
Optical frequency
2.71 (
jj
c)
Varies with composition
2.69 (
|
c)
heterogeneity in the composition due to incompleted an reaction resulting from
small diffusion coefficients of ions within solids.
The wet chemical method is a relatively easier method for obtaining HAp.
Besides, the reaction in any living organisms may occur in aqueous solutions at
low temperatures. Many experiments on the preparation of HAp by this method
have been reported which investigate the formation mechanism of any calcium
phosphates in vitro, in addition to in vivo. The powders prepared by this method,
however, do not seem to be appropriate as the starting materials for ceramics
because they are usually less crystallized, heterogeneous in composition, and
irregularly formed. Sol
gel, alkoxide, and other chemical methods have also been
